Background: Since 1999 the World Health Organization (WHO) recommended the assessment of sperm morphology by Kruger strict criteria (KSC). The manual of WHO contains the cut off values of sperm morphology measured by KSC for normal subject and patients treated by in vitro fertilization (IVF) and intra- cytoplasmic sperm injection (ICSI) without any information regarding intrauterine insemination (IUI). Objectives: The objective of this study is to achieve two major goals that are:1- Assessment of sperm morphology by applying KSC, using two different biological stains, named commercially Testsimplets (TS)pre-stained slides and Sperm-O-Scan (SOS)stain 2- To have a cut off value for morphologically normal sperm that resulting into a successful IUI outcome. Materials and Methods: Fifty five unselected couples attending the Institute of Embryo Researches and Infertility Treatment were included in this prospective study from December 2007 till August 2008. The mean age of male partner was 31.7±1.87years with an average duration of 6.25±1.65years of infertility. The women were prepared for IUI. All the males were subjected to semen analysis with in vitro sperm activation using layering swim-up technique. Assessments of the morphologically normal sperm (MNS) of the samples were performed by using both, High power field and KSC by using TS and SOS stains before and after the activation. Correlation of the positive IUI results and MNS by KSC waw recorded denoting the cut off value for successful results. Results: The mean of morphologically normal sperm applying KSC with the use of SOS stain before in vitro sperm activation was 16.10% and after activation was 37.85% and by using TS stain before in vitro sperm activation was 15.14% and after activation was 37.09%. No significant (P>0.05) differences was detected between the results of MNS of the two stains. The result of IUI was 11 positive pregnancies out of the 55 cases. The mean of MNS using KSC for these positive cases was 11.58% and 12.84% for SOS and TS stains, respectively. Conclusions: The cut off value of MNS by applying KSC and using two different biological stains for a successful IUI program was 11.58% by SOS stain and 12.84% by TS pre-stained slides. Although the study found no statistical differences between the two stains, TS found to be easier, simpler and less time consuming technically than SOS stain.