OBJECTIVE: To explore the effects of nandrolone phenylpropionate (NP) on the expression level of pro alpha 1 (I) collagen after burn in rats and the possible mechanism involved in the process. METHODS: Thirty-two Wistar rats with a deep second-degree scald injury and 20% of total body surface area were randomly divided into two groups to receive either 5 mg/kg NP(NP group) or normal saline (control group) every other day. We analyzed the mean integrated optical density(mIOD) of androgen receptor (AR) to determine the distribution and expression of AR in fibroblasts by immunohistochemistry, and measured expression level of pro alpha 1 (I) collagen mRNA by quantitative fluorescent RT-PCR to find the relation between expressions of AR and pro alpha 1 (I) collagen mRNA. The total specimens were obtained from the scalded rats after 4, 7, 14 and 21 of after burn. RESULTS: The expression of pro alpha 1 (I) collagen mRNA in NP group was significantly higher than that in control group on the 7th, 14th and 21st days(P lt; 0.05), but there was no significant difference on the 4th day. The density of AR in fibroblasts had significant difference (P lt; 0.05) between the two groups after 4, 7, 14 and 21 days. A positive relationship existed between the expression of pro alpha 1 (I) collagen mRNA and quantity of AR in fibroblasts(r = 0.836). CONCLUSION: The nandrolone phenylpropionate increased the expression of pro alpha 1 (I) collagen mRNA and enhanced the density of AR in fibroblasts. The higher expression of pro alpha 1 (I) collagen mRNA had a relation with the change of quantity of AR in fibroblasts.