Nitrification and denitrification in the different layers of the integrated vertical flow constructed wetlands (IVCW) are studied. The results show the constants rate of nitrification and denitrification in the strata of IVCW were 0.01 similar to 6.35 mu g.(g.d)(-1) and 3.37 similar to 4.19 mu g.(g.d)(-1) respectively. The most probable number (MPN) method are employed to determine the number and distribution of nitrifying and denitrifying bacteria in the strata of the system. The results show that the numbers of nitrifying and denitrifying bacteria were 7.5 x 10(3) similar to 1.1 x 10(5) MPN.g(-1) and 7.5 x 10(6) similar to 1.1 x 10(7) MPN.g(-1) respectively. The positive correlation between bacteria and their action was obvious (r = 0.9661, P < 0.001, r = 0.7722, p < 0.025). It is also observed that the number of nitrifying bacteria and nitrification rate was decreased along the direction of the water in the IVCW, while denitrifying bacteria and denitrification rate was increased. And there was the significant negative correlation between nitrification and denitrification rate( r -0.9776, p < 0.001).