This study was conducted through 1996-1999 years in the Department of Pomology, Faculty of Agriculture, Alexandria University. The work involved in vitro callus formation from different seedling (grown in vitro) explants  of sour orange. The main results can be summarized in the following points: 1- On the MT (1969) medium containing 10 mgl^-1 NAA + 0.5mgl^-1 kinetin, the percentages of callus formation from shoot tip, epicotyl, hypocotyl and cotyledon explants (excised from seedlings of sour orange grown in vitro) were 66.67%, 80.00%, 66.67% and 93.33%, respectively. These results indicated that cotyledon segments were the best explants for callus formation. 2-    Maintenance of continually growing for the produced callus by subculturing on the same medium without plant hormones.