The experiments have revealed that (NH)SOcombined with KNOat low concentrationis of advantage to the formation, growth and differentiation of pollen callus in rice,whereas the high concentration of (NH)SO, whether used separately or in combinationwith KNO, obviously inhibits the pollen callus formation. The optimum NH~+ concen-tration is about 7.0 mM (equal to 3.5 mM (NH)SO). A basic medium containing3.5 mM (NH)SOand 28 mM KNOas nitrogen sources has been established. On suchmedium the frequency of the pollen callus formation is higher than that on Miller’s me-dium, and the differentiation of shoot from pollen callus is satisfactory.