Abstract: This study was conducted to evaluate if the efficiency of porcine In Vitro Fertilization (IVF) could be improved by a short co-incubation time for spermatozoa-oocytes using commercial Liquid Stored (LS) boar semen. For this study, LS semen was supplied weekly from the Veterinary Service Laboratory (Department of Livestock Research, Yong-in, Gyeonggi-do, Republic of Korea) and kept at 17°C for 5 days. A total of 808 immature cumulus-oocyte complexes from six replicates were matured in vitro and inseminated with LS semen (5x10⁵ mL^-1 sperm concentration) for 5, 20, 90 or 360 min (control group). To evaluate the developmental competence of each group, all IVF embryos were examined for the following: fertilization rate, cleavage rate, blastocyst formation rate and cell numbers. The oocytes from the 5, 20 and 90 min co-incubation periods were washed in IVF medium (mTBM) to remove spermatozoa, transferred to another droplet of the same medium (containing no spermatozoa) and incubated until 6 h post-insemination. Thereafter, all IVF embryos were cultured in porcine zygote medium-3 for 10 h after insemination to assess fertilization parameters. A co-incubation period of 5 min resulted in a significantly (p<0.05) lower spermatozoa penetration rate (66.8%) as compared with 20, 90 and 360 min (91.8, 100 and 100%, respectively) but there was no difference in Male Pronucleus (MPN) formation rate. Co-incubation for 5 and 20 min resulted in a significantly higher monospermy rate (39.7 and 38.4%, respectively) as compared with the 90 min incubation (4.2%) while no monospermic oocytes were observed in the 360 min group. The polyspermy rate was significantly higher with co-incubation periods of 90 and 360 min (95.8 and 100%, respectively) as compared with 5 and 20 min (60.3 and 57.8%, respectively). The mean number of penetrating spermatozoa per oocyte was significantly lower in the 5 and 20 min groups (1.7 and 2.3, respectively) as compared with the 90 and 360 min groups (9.2 and 17.6, respectively). The efficiency of fertilization (number of monospermic oocytes/total number of inseminated oocytes) was significantly higher in the 20 min (35.8%) co-incubation period as compared with the other groups (25.1 and 4.2% for 5 and 90 min, respectively). The cleavage rate for the 5 and 20 min (52.5 and 65.6%, respectively) groups was significantly higher than the 90 and 360 min groups (32.1 and 10.5%, respectively). The 20 min (18.8 and 113.2%) co-incubation period resulted in a significantly higher blastocyst formation rate and total blastocyst cell number compared to the 90 min group (3.6 and 68.0%) but there was no significant difference between the 5 min (10.7 and 90.3%) and 20 min groups. The embryos in the 360 min co-incubation period did not develop into blastocysts. Concerning cell numbers, blastocysts that developed with the 20 min (24.6) co-incubation period had a greater number of cells in the inner cell mass than the 5 min (12.4) group however, there was no difference in the number of trophectoderm cells and total cell number. Therefore, researchers recommend a two-step IVF procedure for porcine oocytes with a co-incubation period with spermatozoa for 20 min followed by an additional culture until 6 h without spermatozoa when using commercial LS semen for porcine IVF experiments.