Abstract: To understand the relationship between the IGF-I and the porcine fertility development, testicular tissue samples were collected from male Erhualian and Large White pigs at 0, 3, 20, 30, 90, 120 and 180 days of age respectively. IGF-I and IGF-IR mRNA level were determined by relative quantitative RT-PCR with 18S rRNA as an internal standard. The developmental pattern of testicular IGF-I mRNA expression in Erhualian boars was similar with those in Large White boars from day 0 to 30, which increased with the age of boars. The levels of IGF-I mRNA in Erhualian boars had no significant changes from day 30 to 180, while those in Large White boars showed a temporal drop at day 90 and restored to the level of day 30 thereafter (P﹤0.05 ). Overall IGF-I mRNA level was higher in Erhualian boars than in Large White boars (P﹤0.05 ). The patterns of testicular IGF-IR mRNA expression in Erhualian and Large White boars were different. The levels of IGF-IR mRNA in Erhualian boars maintained consistent in general throughout the period of investigation, despite a tendency of decrease observed from day 90 to 120 (P﹤0.05 ). IGF-IR mRNA levels in Large White boars was high at day 0 and declined at day 3 (P﹤0.05 ) , and maintained invariable thereafter. Overall IGF-IR mRNA level was higher in Erhualian boars than in Large White boars (P﹤0.05 ). Testicular IGF-I mRNA level was found to be positively correlated with IGF-IR mRNA level (r=0.575, P<0.01). The results suggest that IGF-I and IGF-IR mRNA in porcine testis are coordinately expressed according to breed-specific developmental patterns, and it may be important in porcine testis development.