Abstract: Experiments were made to compare the applications of quicklime,croton seeds and tea seed cake as“sterilizers”of fish ponds,and the following facts were observed: For the purpose of killing the wild fishes,experiments have decidedly disclosed that the quicklime is the most effective one.With a concentration of 75 kg.per mou,in 10-15 cm.depth of water,it kills all kinds of fishes very promptly and thoroughly.The tea seed cake,which had been tested out of a concentration of 12.5 kg.per mou,has an efficiency slightly weaker than the quicklime,and the traditional croton seeds(2—2.5 kg.per mou,in 33-66 cm. depth of water)are the weakest of the three.They are very difficult to clean out all the carp(Carassius auratus)in the pond. Quicklime kills the large-sized aquatic animals,such as frog eggs,tadpoles, crabs,mussels shrimps,chironomus larvae and leeches etc.very readily.We have also noticed that it tends to kill the filamentous algae and some tender water vascular bundle plants that are usually present in the shallow ponds.Tea seed cake has the same effect as quicklime on large-sized aquatic animals, but as to the algae and water plants,it appears no effect.The croton seeds, on the other hand,show no sign of violence to them As to the plankton,we have found that quicklime will at first kill all the vegetative forms of phyto- and zooplanktons that occur in the pond. Four days after,the planktons become gradually grow out and reaching their maximum luxuries on the 8-9th day.There is no great difference in the number of planktons after the tea seed cake was applied,though it will increase gradually(but will never be as high as the quicklime).Contrary to the quick-lime,the action of croton seeds increases the number of plankton very greatly at the very beginning and drops abruptly down as the time elapsed. To test the efficiency of the“sterilization”on the pathogenetic bacteria of these three dements,we made ordinary agar plat medium to culture the water samples before and after the application of these drugs.It is proved that only quicklime is effective.Croton seeds have no inhibiting action and the tea seed cake seems to encouraging the bacterial growth. Quicklime increases the pH value very greatly when adding into the water,and decreases gradually.The optimum point for the growth of the plankton is between 9.0—9.4.Croton seeds increase the pH value slightly but there can hardly be found any correlations between the growth of plankton. The tea seed cake has the same effect as the quicklime but in very low intensity. Through a series of experiments in large“kongs”full of the water anti then in ponds,we found that in an average of 1 m.depth of water to use 212.5—225 kg.of quicklime per mou has the same good result as empty pond “sterilization”.This finding enables the practice more easily and economically.