Abstract: Hypocotyl, cotyledon, leaf blade and leaf petiole explants of tomato were cultured on MS medium supplemented with 2.0mg/L BA and 0.2mg/L IAA for induction of callus and bud formation. Histological observations on callus and bud formation were carried out. The following results were obtained: there were significant difference in callus induction and growth among above mentioned 3 kinds of explants, calli from hypocotyl and cotyledon explants were induced earlier than others, and grew faster than others. Buds differentiated from calli were adventitious buds. Adventitious buds were generally formed on the peripheral parts of the calli, also originated from the cambium like cells surrounded by the vascular nodules. Adventitious roots originated from the pericycle. The caryological observation on callus paraffin section showed that, in the course of callus formation from cotyledon there were more kinds of nuclear division modes than hypocotyl calli, but all these were of amitosis.