Correlations have been developed for obtaining the isotopic composition of Pu produced in Indian research (CIRUS, DHRUVA) and power (PHWR) reactors. The experimental data obtained on 238Pu/(239Pu + 240Pu) alpha activity ratio using alpha spectrometry and on 240Pu/239Pu,241Pu/239Pu, 242Pu/239Pu atom ratios by thermal ionisation mass spectrometry were used for developing isotope correlations.