Abstract: Objective:To explore the protective effect and mechanism of dietary n-3 polyunsaturated fatty acid supplements on dermal collagen of aged skin in rats. Methods:Young skin was taken from dorsal skin of 9-month-old rats. Aged skin was taken from 22-month-old rats which were fed with n-3 PUFAs diet (aged n-3 PUFAs group) or control diets (aged control group). Pathologic HE staining, Masson staining and Weigert staining were applied to observe the structure of skin, collagen and elastic fibers. The expression of type and Ⅲ collagen and the mRNA expression levels of type Ⅰ, Ⅲ, Ⅳ, Ⅴ collagen and MMP1, MMP3, MMP9, MMP10, MMP13 of the three groups were compared by ELISA and RT-qPCR. Results:The epidermis of the naturally aged skin was flattened and the dermal collagen fibers were arranged in disorder compared with the young skin. The expression of type Ⅰ and Ⅲ collagen reduced in aged rat skin compared to young skin (P<0.05). The mRNA expression levels of type Ⅰ, Ⅲ, Ⅳ, and Ⅴ collagen in the dermis of aged rats were lower than those in the young rats (P<0.05), and mRNA expression levels of type Ⅰ and Ⅲ collagen in the aged n-3 PUFAs group were higher than those in the aged control group (P<0.05).The mRNA expression levels of MMP1, MMP9, MMP10 and MMP13 in aged skin were significantly higher than those in young skin (P<0.05). The mRNA expression levels of MMP10 and mmp13 in aged n-3 PUFAs group were significantly lower than those in aged control group (P<0.05). Conclusion:Dietary n-3 PUFAs supplementation could promote the synthesis of type Ⅰ and Ⅲ collagen, and reduce the expression of MMP10 and MMP13, thereby increasing the content of type Ⅰ and Ⅲ collagen in aged skin and delaying the natural aging process of the skin.