Objective: Investigate characteristics of spermatozoa and these related factors in case of male infertility due to oligozoospermia. Methods: A crosssectional study was performed in 500 cases of male infertility due to oligozoospermia at National Hospital of Obstetrics and Gynecology. Results and Conclusions: for all samples, alive sperm rate is less than 75 percent, lower the standard of WHO and abnormal sperm rate is 41 percent, higher the standard of WHO (1999). Some related factors to quality of sperm are: 54.6 percent smoking, 21 percent contacting with chemicals, 21 percent keep sitting for a long time and 26.4 percent got sexually transmitted diseases.