Objective: To evaluate whether co-culture of oocytes on vero cell monolayers from Day 0 (Day 0 group) after egg retrieval results in an increase in developmental capacity such as fertilization rate, embryo quality, blastulation and clinical pregnancy rate compared with co-culture of oocytes from Day 1 (Day 1 group). Methods: Sperms were treated with Hams F-10 supplemented with 10% human follicular fluid (hFF). Vero cells for co-culture were prepared in TCM-199 with 10% FBS. Oocytes were co-cultured from Day 0 and fertilized oocytes were co-cultured from Day 1 on vero cell monolayers in DMEM with 10% and 20% hFF, respectively after egg retrieval. On day 1, 2 and 5, fertilization rate and grade of embryos and blastocysts were evaluated. Results (fertilization rate, cleavage rate, grade of embryos and blastocysts and pregnancy rate) were considered statistically significant when p value was less than 0.05 using t-test and $x^2$. Results: In sibling oocytes of same cycles, no differences were found in fertilization rate (94.6 vs. 91.4%), cleavage rates (94.6 vs. 91.4%), embryo grade (on day 2 and 3) and blastulation (65.6 vs. 57.0%) and their grade. In different oocytes of different cycles (patients), no differences were found in fertilization (79.8 vs. 78.3%), cleavage rates (77.7 vs. 76.4%) and blastulation (56.0 vs. 45.3%), but pregnancy rate was higher in the Day 0 group than in the Day 1 group (60.0 vs. 42.9%). Conclusions: This study revealed that the embryonic development capacities were not affected by the different co-culture time in the sibling oocytes of same cycles. Although no statistical significance, because of small size of study, there was a trend for higher pregnancy rates in Day 0 group compared to Day 1 group in different oocytes of different cycles.