This paper analysed 102 strains of adenovirus types 3(Ad3) and 7(Ad7) causing infant pneumonia from 1976 to 1988 in northern China. Two genotypes of Ad7, 7b and 7d, were identified by using restriction endonucleases, BamHI, BcLI, BgLI, SmaI, XbaI and HindIII. 3 genotypes of Ad3, 3I, 3II and 3III, were identified by using BgLII and BamHI. Of 56 Ad7 strains, 34 were 7b (76.8%) spread over last 10 years; 13 7d(23.2%) occurred from 1982, together with 7b. Of 46 Ad3 strains, 42 3I(91.3%) spread over the past 12 years. 3II and 3III scattered all over these years. Ad3I and Ad7b were the dominant genotypes. The results indicated that Ad7d tended to increase with time from 1982. It is possible that Ad7d will become dominant genotype and replace Ad7b.