diff --git a/CommandLines.cpp b/CommandLines.cpp
index 2af9327..256a35a 100644
--- a/CommandLines.cpp
+++ b/CommandLines.cpp
@@ -79,6 +79,8 @@ static ko_longopt_t long_options[] = {
     { "chem-c",     ko_required_argument, 361},
     { "chem-f",     ko_required_argument, 362},
     { "ul-m",     ko_required_argument, 363},
+    { "rl-cut",     ko_required_argument, 364},
+    { "sc-cut",     ko_required_argument, 365},
     // { "path-round",     ko_required_argument, 348},
 	{ 0, 0, 0 }
 };
@@ -228,6 +230,10 @@ void Print_H(hifiasm_opt_t* asm_opt)
     fprintf(stderr, "                 detect chimeric reads with <=INT other reads support [%lu]\n", asm_opt->chemical_cov);
     fprintf(stderr, "    --chem-f     INT\n");
     fprintf(stderr, "                 length of flanking regions for chimeric read detection [%lu]\n", asm_opt->chemical_flank);
+    fprintf(stderr, "    --rl-cut     INT\n");
+    fprintf(stderr, "                 filter out ONT simplex reads shorter than <INT> for assembly [%ld]\n", asm_opt->rl_cut);
+    fprintf(stderr, "    --sc-cut     INT\n");
+    fprintf(stderr, "                 filter out ONT simplex reads with a mean base quality score below <INT> [%ld]\n", asm_opt->sc_cut);
 
 
     fprintf(stderr, "Example: ./hifiasm -o NA12878.asm -t 32 NA12878.fq.gz\n");
@@ -364,6 +370,9 @@ void init_opt(hifiasm_opt_t* asm_opt)
     asm_opt->chemical_cov = 1;
     asm_opt->chemical_flank = 256;
     asm_opt->ul_mod = 0;
+
+    asm_opt->rl_cut = 1000;
+    asm_opt->sc_cut = 10;
 }   
 
 void destory_enzyme(enzyme* f)
@@ -990,6 +999,10 @@ int CommandLine_process(int argc, char *argv[], hifiasm_opt_t* asm_opt)
         } else if (c == 363) {
             asm_opt->ul_mod = atol(opt.arg); 
         **/
+        } else if (c == 364) {
+            asm_opt->rl_cut = atol(opt.arg);
+        } else if (c == 365) {
+            asm_opt->sc_cut = atol(opt.arg);
         } else if (c == 'l') {   ///0: disable purge_dup; 1: purge containment; 2: purge overlap
             asm_opt->purge_level_primary = asm_opt->purge_level_trio = atoi(opt.arg);
         }
@@ -1027,6 +1040,9 @@ int CommandLine_process(int argc, char *argv[], hifiasm_opt_t* asm_opt)
 
     // fprintf(stderr, "[M::%s::] post join::%u\n", __func__, (uint32_t)(!(asm_opt->flag & HA_F_BAN_POST_JOIN)));
     // exit(1);
+    if(!(asm_opt->is_ont)) {
+        asm_opt->rl_cut = -1; asm_opt->sc_cut = 1;
+    }
 
     return check_option(asm_opt);
 }
diff --git a/CommandLines.h b/CommandLines.h
index 511a5f5..3bebc87 100644
--- a/CommandLines.h
+++ b/CommandLines.h
@@ -5,7 +5,7 @@
 #include <pthread.h>
 #include <stdint.h>
 
-#define HA_VERSION "0.25.0-r721"
+#define HA_VERSION "0.25.0-r726"
 
 #define VERBOSE 0
 
@@ -166,6 +166,10 @@ typedef struct {
     uint64_t is_sc;
     uint64_t chemical_cov;
     uint64_t chemical_flank;
+
+    int64_t rl_cut;
+    int64_t sc_cut;
+
 } hifiasm_opt_t;
 
 extern hifiasm_opt_t asm_opt;
diff --git a/htab.cpp b/htab.cpp
index d268df4..bd16ded 100644
--- a/htab.cpp
+++ b/htab.cpp
@@ -546,6 +546,21 @@ const int ha_pt_cnt(const ha_pt_t *h, uint64_t hash)
 	return kh_key(g->h, k) & YAK_MAX_COUNT;
 }
 
+inline uint64_t flt_quals(char *sc_a, uint64_t sc_l, uint64_t sc_off, int64_t sc_cut)
+{
+	int64_t sc_min = sc_l * sc_cut, sc_tot; uint64_t k;
+	for (k = sc_tot = 0; (k < sc_l) && (sc_tot < sc_min); k++) {
+		sc_tot += (((uint8_t)sc_a[k]) - sc_off);
+	}
+
+	// if(sc_tot < sc_min) {
+	// 	fprintf(stderr, "[M::%s] sc_tot::%ld, sc_min::%ld, sc_l::%lu\n", __func__, sc_tot, sc_min, sc_l);
+	// }
+
+	if(sc_tot < sc_min) return 0;
+	return 1;
+}
+
 /**********************************
  * Buffer for counting all k-mers *
  **********************************/
@@ -745,7 +760,8 @@ static void *sf##_worker_count(void *data, int step, void *in) /** callback for
 		} else {\
 			while ((ret = kseq_read(p->ks)) >= 0) {\
 				int l = (int)(p->ks->seq.l) - (int)(p->opt->adaLen) - (int)(p->opt->adaLen);\
-				if(l <= 0) continue;\
+				if((l <= 0) || (l < asm_opt.rl_cut)) continue;\
+				if((asm_opt.is_sc) && (asm_opt.sc_cut > 0) && (!flt_quals(p->ks->qual.s+p->opt->adaLen, l, 33, asm_opt.sc_cut))) continue;\
 				if (p->n_seq >= 1<<28) {\
 					fprintf(stderr, "ERROR: this implementation supports no more than %d reads\n", 1<<28);\
 					exit(1);\