Test day milk yield records (5130), milk production and milk composition traits from 19 lactations of Gir cows collected for two years (2019 and 2020) were used to understand the performance of Gir breed in hot and humid conditions of Tamil Nadu. Different lactation curve models were used for modelling test day records and model diagnostics like adjusted R-square, BIC and RMSE were used to obtain the model of best fit. The mean test day yield, fat per cent, SNF (%), total milk yield, peak yield, days to attain peak yield and calving interval observed were 5.78 kg, 5.05%, 7.65%, 1507 kg, 9.23 kg, 46.5 days and 447 days respectively. Ali and Shaeffer model offered the best fit for lactation curve in Gir cows. Mahadevan method and Gamma function were used to calculate the persistency of milk yield which was obtained as 1.33 and 6.348 respectively. Results of the study indicated that Gir cattle were able to adapt themselves through maintenance of reproductive traits comparable with that of the native tract but the new humid environment has caused a slight decrease in the performance of milk production traits.