Objective:To investigate the mechanism of hypertrophic scar formation in different age periods.Methods:The expression of type I and type Ⅲ collagen of hypertrophic scar in different age periods was measured with immunohistochemistry which was divided into two groups 1～19 years old and 20～50 years old

and the same measure was adopted in normal skin divided into four groups-fetal

1～19

20～50

and more than 60 years old .The quantities of type I and type Ⅲ collagen and the ratios were analyzed.Results:①The ratio of type Ⅰ/type Ⅲcollagen of normal skin had a guadually increasing tendency.②The ratio of type Ⅰ/type Ⅲ collagen of HTS was increasing compared with normal skin(NS)

and relative quantities of type I collagen of HTS was significantly increasing.The ratio of type Ⅰ/type Ⅲcollagen of HTS in group of 1～19 year old was highter than that in the group of 20～50 year old .Conclusion:Normal structure of the skin is decided by quantities and ratio of type I and type Ⅲ collagen.The formation of hypertrophic scar in different age periods relates to maladjustment of the ratio of type I and type Ⅲ collagen.Collagen synthesis and regulation of its constitute are finished after about six months.They keep relatively stable within 6 month to 2～3 years.