Abstract: To identify the mechanisms that citrus protoplasts from different origins hold different regeneration capacity，O2 - production rate，content of malonaldehyde（ MDA），glutathione（ GSH） ，ascorbic acid（ AsA）， and activity of superoxide dismutase（ SOD），catalase（ CAT） and peroxidase（ POD） were analyzed during the maceration period. Results showed that both the O2 - production rate and MDA content of recalcitrant leaf mesophyllderived protoplasts were higher than those of callus protoplast at the same time of protoplast isolation. The change trend of SOD activity of callus protoplasts was similar to that of O2 - production rate，i.e.，an increasing trend during the maceration period. However，the SOD activity of leaf protoplasts decreased significantly after 12 h of protoplast isolation. At the same time after protoplast isolation，the CAT activity of callus protoplasts was significantly higher than that of leaf protoplasts，and the contents of GSH and AsA of callus protoplasts was also higher than those of leaf protoplasts. Therefore，citrus protoplasts derived from different tissues had different regeneration capacity，could be due to the metabolic balance of active oxygen species（ AOS），protective enzyme and antioxidants，i.e.，AOSgeneration and defense systems in cells.