Purpose: The purpose of this study was to determine the efficacy of low-and large-volume techniques of intrauterine insemination (IUI) on pregnancy rates in unexplained infertility couples. Materials and Methods: This retrospective study was performed in a single center over a 33-month period which included a total of 272 couples that underwent 272 IUI cycles that were divided into two groups. Low-volume group underwent 0.5 ml of inseminated semen; large-volume group underwent four ml of inseminated semen. The clinical pregnancy rates per cycle in each age group were evaluated. Results: In the large-volume group, clinical pregnancy rates were higher. In <= 34 age groups, clinical pregnancy rates were higher in large-volume group while in > 35 age group, clinical pregnancy rates were higher in low-volume group. Conclusion: This study clearly demonstrated the effectiveness of large-volume technique on IUI success in < 35 age women with unexplained infertility.