The relationship between predator and prey is one of the hot topics in ecological research. To study the quantitative relationship between rodents and hawks in typical steppe, we investigated the density of rodents and hawks at 15 experimental areas in Abagaqi, Xilinguole League, Inner Mongolia during July 2005. By using standard killing trap method, we estimated the density of rodents; at the same time, we observed and counted the density of hawks. Altogether 2 675 rodents were captured, and hawks were observed for 450 times (Table 1). The regression analysis showed that the density of rodents had significantly impact on the density of hawks. This relationship between rodents and hawks, which is in line with the sigmoidal S-shaped curve, can be fitted by Gompertz model, W = 22.765 e - 3.735 e - 0.078 t, goodness-of-fit (R2) is 0.984 (Fig. 1a). The growth of hawks was extremely slow at the initial stage, then rapidly increased to maximal value as the rodent density increase until an inflexion was showed. After then hawk density kept stable (Fig. 1b). This finding is agree with the viewpoint that the numerical response of vertebrate predators to preys could be simulated by the models of Holling-Ⅲ. According to our results, the functional response can be roughly divided into three stages: (1) the steady phase, that the activity of hawks slowly grows as the density of rodents increases; (2) the rapid reaction phase, hawks increase their activiey rapidly as rodents density exceeds 5 ind/hm2; (3) the stable platform phase, the activity frequency of hawks is stable when the density of rodents reaches about 40 ind/hm2 and over. Our results can provide reference for the rodent density controlling by their natural enemies.