【Background】Catopsilia pyranthe L. is one of the major pests of garden plants, cassia (Cassia corymbosa), yellow cassia (Cassia alata L.), and chestnut trees (Cassia siameaL.). 【Method】The flight and oviposition behavior of C.pyranthe were observed on cassia plants in the butterfly ecology garden of Sanming City, Mingxi County, Fujian Province. 【Result】The flight activity and egg-laying behavior of the adult Catopsilia pyranthe was significantly (R=0.9406) correlated. The species was most active in the morning hours (08:00~11:00) and laid most eggs during this period. Most eggs were deposited on the leaves, with no difference between upper and lower leaves. Single eggs were found laid on the bud shoot, stem, flowers of cassia plant. The butterflies laid their eggs mostly on the second and the third compound leaves gradually decreasing on other, and none were found on the sixth compound leaves. The butterfly laid eggs on the leaflets of the end of fronds, and the numbers of eggs near the leaflet were gradually reduced. Equal number of eggs were laid on potted cassia plants and on branches cut off the plant and kept in a hydroponic solution. 【Conclusion and significance】The flight activity correlates well with egglaying and is a suitable method to monitor the pest potential under field conditions.