Introduction: Intracytoplasmic sperm injection (ICSI) is a widely used adjunct to in vitro fertilization (IVF) for male-factor infertility when fertilization failure is suspected. In patients with borderline semen, the decision to choose either IVF or ICSI is critical because the chance of total fertilization failure after a conventional IVF or of performing an unnecessary ICSI procedure is hard to predict.   Objective: The purpose of this study was to assess the value of the allocation of some eggs to ICSI and others to conventional insemination (Split ICSI/insemination) in IVF cycles in which semen parameters are subfertile.   Design: It is prospective study.   Materials and methods: Between August 2007 and April 2010, 190 patients had half of their eggs inseminated with ICSI and the other half inseminated with conventional IVF.   Results:  In this study, 76.3% of patients were fertilized by both IVF and ICSI, 21.6% of patients were fertilized only by ICSI while 2.1% of patients were not fertilized either by IVF or ICSI. Fertilization rate was significantly higher in oocytes injected by ICSI (63.7%) compared to oocyte inseminated by IVF (44.3%). In patients fertilized by both IVF and ICSI, although ICSI fertilization rate was higher (65.9%) than IVF fertilization rate (57.3%), yet there is no significant differences were observed. High grade embryos were significantly higher in oocytes injected by ICSI (75.9%) compared to oocyte inseminated by IVF (56.4%). Also, significantly more type 1 and 2 embryos developed after ICSI compared with IVF (77.3% vs. 56.4%) in the group of patients with fertilization after both IVF and ICSI.   Conclusion: According to our findings, implementation of ICSI in couples with mild male factor infertility could improve fertilization rates and decrease the risk of complete fertilization failure. Additionally, split ICSI procedure provides valuable clinical information about fertilization potential for the couple and unnecessary use of ICSI procedure can be avoided in future cycles for patients who have achieved good fertilization in both IVF and ICSI.