Indoor radon, thoron, and their progeny concentrations were measured in Mokokchung district of Nagaland, India over three different seasons by using Direct Radon and Thoron Progeny Sensors and pinhole type radon-thoron discriminating dosimeters. The indoor radon and thoron concentrations were found to vary between 44 ± 6–75 ± 16 Bqm⁻³ and 25 ± 2–62 ± 49 Bqm⁻³ while their corresponding progeny concentrations varied between 3.2 ± 2.1–17.3 ± 8.7 Bqm⁻³ and 0.21 ± 0.06–1.49 ± 0.86 Bqm⁻³ respectively. Based on the study, it was found that the inhalation dose varied between 0.35 and 1.64 mSvy⁻¹ and are within the recommended values as suggested by ICRP, 2018. The equilibrium factor (E.F) varied from 0.06 to 0.29 for indoor radon and 0.01 to 0.02 for indoor thoron.