Tritium (³H) is one of the important long-lived radioisotopes in the gaseous effluent released from Pressurised Heavy Water Reactors (PHWR). For the first time, the studies on diurnal variation of atmospheric tritium concentration was carried out using an in-house developed automatic air moisture collection sampler at Kakrapar Gujarat site, India, where PHWRs are operational. Correlation of diurnal variation of atmospheric tritium concentration with meteorological parameters such as absolute humidity, ambient temperature and wind speed is studied and presented in this paper. Positive and significant correlation of atmospheric ³H concentration was observed with respect to the absolute humidity. Negative correlation was observed in ambient temperature and wind speed. The diurnal maximum and minimum of ³H concentration was found during 21.00–23.00 h (night) and 13.00–16.00 h (day), respectively.