Plaque samples were collected from tooth surface by the sampling method in 28 volunteers (two groups, 14 young people, ages ranged from 19-26 years, mean: 22.29 years old; 14 old people, aged between 60-70 years, mean: 64.35 years old, DMFT > 3). The activity for three enzymes including amylases, LDH, GTF was tested by micro-chemistry enzyme analysis method. The results showed that there were no significant difference for the activity of three enzymes in two groups (P > 0.05). The finding suggests that dental plaque is a specific microecologic environment and cariogenic factor, age does not affect the activity of enzymes, plaque in different ages has similar cariogenicity.