Objective To investigate the expression of AT2R and myocardial collagen in heart of different age spontaneously hypertensive rats( SHR) and to explore the role of these factor in the development of hypertension． Methods Male SHR( n = 30) were allocated to five groups by age: 1) one-month-old group( S1) ; 2) two-month-old group( S2) ;3) three-month-old group( S3) ; 4) six-month-old group( S6) ; 5) nine-month-old group( S9) ． Sex and age matched WistarKyoto normotensive rats( WKY) served as controls． Blood pressure was measured． Plasma concentration of angiotensinⅡ ( Ang Ⅱ ) was measured by radioimmunoassay ( RIA ) ． The expression of AT2R in heart was examined by immunohistochemistry and computer image analysis． Collagen of the heart was stained by sirus red to observe the myocardial fibrosis． Results 1． An age-dependent increase of SBP was observed in SHR before six months( P ＜ 0. 05) ，the SBP was higher in the different age SHR than that in the matched WKY( P ＜ 0. 05) . 2． Plasma AngⅡconcentration was higher in S2，S3，S6 and S9 than that in S1( P ＜ 0. 05) ，plasma AngⅡ concentration was higher in S2，S3，S6 and S9 than that in the matched WKY ( P ＜ 0. 05 ) . 3． The quantification of AT2R immunohistochemical staining showed: An age-dependent decrease of the AT2R was observed in heart in SHR( P ＜ 0. 05) ，which was lower in S9 than that in S1( P ＜ 0. 05) ，The AT2R levels were lower in SHR than those in the matched WKY( P ＜ 0. 05) . 4． The content of collagen in the heart of SHR showed: An age-dependent increase of the myocardial fibrosis was observed in SHR ( P ＜ 0. 05 ) ． Conclusions The expression of AT2R protein in heart of SHR is decreased compared with WKY． The content of collagen in the heart of SHR is increased compared with WKY． An age-dependent varies of AT2R protein and the content of collagen was observed in SHR．