Abstract: To investigate the spatial and temporal expression profiles of seminal plasma motility inhibitor (SPMI) gene in the genital tracts of boars and gilts, the qualitative RTPCR was used to detect tissue expression pattern along reproductive tracts and semiquantitative RTPCR was applied to determine the developmental expression of SPMI in seminal vesicle and bulbourethral gland in the current study. The qualitative RTPCR revealed that the expression of SPMI mRNA was highest in seminal vesicle, moderate in bulbourethral gland and uterine horn, weak in prostate, cervix and ovary, no signal was found in the other reproductive tissues. The semiquantitative RTPCR revealed that the similar developmental expression pattern of SPMI in seminal vesicle and bulbourethral gland was found, and the expression of SPMI both in seminal vesicle and bulbourethral gland initiated on day 1 and improved until sexual maturity (150 d) with age increase. The expression of SPMI in seminal vesicle increased significantly on days 60, 90 and 150 d (P<0.05); while the expression of SPMI in bulbourethral gland increased significantly on days 30, 90 and 150 d(P<0.05), the expression increased on day 60 d compared with that on day 30 d, but the difference was not significant (P>0.05). These results indicate that the SPMI express extensively along the genital tracts of boars and gilts, and in general, the temporal expression of SPMI during boar development is age dependent and the expression level is improved significantly from puberty to sexual maturity.