Scale effects of hydraulic conductivity (K) are often reported from the results of different kinds of field aquifer tests. However, the scale effects of K. values estimated by pumping tests are rarely discussed separately. In this study, field tests, which were conducted in Houzhai karst basin, southwestern China, were used to test the scale effect of K. The support volume and nominal length were separately regarded as the measurement scale. Numerous numerical pumping tests were performed in the hypothetic heterogeneous aquifers to evaluate the scale effect using the estimated K values in pumping tests. The results of the different field tests provided the verification of the scale effect of K. While the nominal length was considered as the measurement scale, the scale effect of K is not significant due to the paucity of field tests. The scale effect of K was reproduced using numerical pumping tests in heterogeneous aquifers, and becomes significant as the heterogeneity of the aquifer increases. With respect to a mildly heterogeneous aquifer in this study, it is difficult to find the sharp increasing trend between K and the measurement scale because the difference between the high K zone and low K zone is relatively small.