AbstractDe‐esterification of mango peel pectin in situ by the action of the enzyme pectinesterase (PE) has been investigated. The rate of enzymic deesterification was highest between pH 8.5 and 9.5 with chemical deesterification also being important. In‐situ PE activity declined with fruit ripening but remained relatively constant when assayed on citrus pectin. The most likely explanation for this difference is a change in suitability of the pectin substrate within the fruit during ripening. A reduction in the degree of esterification (DE) of the pectin to 36‐42% was obtained following incubation of the mango peels at pH 8.5 for 90 min. A crude preparation of exogenous PE from mango peel and lime pulp was incubated at pH 8.5 with heat‐treated (PE inactive) peel as a means of increasing the rate and extent of de‐esterification. The PE activity of both these exogenous enzyme preparations was lower on the peel than that of the in‐situ mango enzyme, but considerably higher on a hot‐water‐soluble fraction extracted from the peel. It is suggested that enzyme solubility and pectin accessibility are the major factors affecting in‐situ de‐esterification of pectin in mango peel.