Objective To investigate the prevalence of Ureaplasma urealyticum(Uu) in infertile male, furthermore, to observe the influence of Uu infection on quality of sperm and antisperm antibody(AsAb). Methods The seminal plasmas of 200 infertile subjects and 100 healthy subjects were analyzed for quality using routine examination. Uu was detected by the liquid medium and the selective solid medium and AsAb in the seminal plasma was assayed by using the method of mixed antiglobin reaction. Results The prevalence of Uu in the infertile males(47.5%) was significantly higher than that in the healthy(21%)(P<0.05). The sperm concentration in Uu-positive infertile group(57.05?33.61)?10⁶/ml was significantly lower than that in Uu-negative infertile group and the healthy group(P<0.01). The vitality and rapid progressive motility in Uu-positive infertile group were(42.77?21.53)% and (29.71?20.45)%, which were significantly lower than those in the healthy group, but there was no significant difference between the two infertile groups. The positive rate of AsAb in Uu-positive infertile group(38.9%) was significantly higher than that in Uu-negative infertile group(18.1%) and the healthy group(7.5%) (P<0.05). Conclusions The prevalence of Uu in the infertile males is high. Uu infections can result in the decrease of the semen quality and the production of AsAb.