In horticulture, water has always been important constraint and in many cases, a rare resource.Certainly, the precise knowledge of the physiological basics of all aspects of water use relations is essential for better understanding of horticultural crops. The following variables viz., photosynthetic rate, stomatal conductance, photosynthetic active radiation, relative humidity percentage of leaves, internal CO₂ concentration, transpiration rate and leaf temperature were evaluated. In this experiment, studies were aimed to evaluate the physiological characteristics of custard apple cv. Raydurg in response to fluctuations in parameters month wise during August to December, 2015. Photosynthetic rates (Pn) ranged from 2.98 to 9.3 mmol m^-2 s^-1; Photosynthetic Active Radiation (PAR) ranged from 859 to 2087; stomatal conductance (Gs) varied between 3.0 to 17.0 m^-2 smol^-1; relative humidity percentage between 5.60 to 12.57 over an active growth season from August to December, 2015.