ABSTRACT:The activities of acid phosphatase and alkaline phosphatase were investigated in two varieties of ripening Carica papaya fruit; Oblong-shaped variety which is also known as 'Agric pawpaw' and Pear-shaped variety which is also known as 'Local pawpaw'. Acid phosphatase activity decreased significantly (p < 0.01) throughout the ripening stages from 0.0186±0.0006 to 0.0037 ± 0.0002µmol/min/g fresh weight in the Oblong-shaped variety: 'Agric pawpaw' and from 0.0134 ± 0.0008 to 0.0068 ± 0.0004µmol/min/g fresh weight in the Pear-shaped variety: 'Local pawpaw'. Conversely, alkaline phosphatase activity was found to increase significantly (p < 0.01) throughout the ripening stages from 0.0044 ± 0.0006 to 0.0135 ± 0.0006µmol/min/g fresh weight in the Oblong-shaped variety: 'Agric pawpaw' and from 0.0074 ± 0.0012 to 0.033 ± 0.0023µmol/min/g fresh weight in the Pear-shaped variety: 'Local pawpaw'. These results suggest that acid phosphatase is the main non-specific phosphatase that is responsible for the production and supply of inorganic phosphate in the unripe stage of Carica papaya fruits, while alkaline phosphatase is responsible for the production and supply of inorganic phosphate in the overripe stage. Acid phosphatase and alkaline phosphatase could be obtained from the unripe and overripe stages of Carica papaya fruits respectively for research purposes, for commercial exploitation and industrial gains. © JASEM http://dx.doi.org/10.4314/jasem.v18 i2.11