Background:Mycoplasma infections are suggested as etiology of adverse pregnancy outcomes. Objective:The aim of this study was to evaluate the association of Mycoplasma hominis (M. hominis) infection and spontaneous abortion among pregnant women.Materials and Methods:In this case-control study that was conducted from August 2012 to January 2013, totally, 109 women were included with spontaneous abortion with gestational ages of 10-20 weeks (Cases), and 109 women with normal pregnancy with gestational ages between 20-37 weeks (Controls) in Sanandaj, Iran. Using specific primers and extracted DNA from endocervical swabs, a PCR test was conducted for detection of M. hominis infection in women. For comparison of qualitative and quantitative variables, independent Fisher tests were used and p<0.05 was considered significant.Results:The total frequency of M. hominis infection was 6 (2.75%) in women. The frequency of M. hominis infection was 2 (1.83%) in the case group (spontaneous abortion) and 4 (3.66%) in the control group, respectively. In both case and control groups, no association was seen between M.hominis infection and spontaneous abortion (OR=0. 49, CI 95%: 0.08-2.73, p=0. 683). Conclusion:M. hominis was positive in the genital tract of some pregnant women, but it was not associated with spontaneous abortion. However, to prevent adverse pregnancy outcomes in women, foetus and neonate, routine screening and treatment for the genital Mycoplasma is recommended.