Natural gamma radiation from radioactive contamination is an important environmental part that may have an effect on ecosystems and human health. Natural gamma radiation exists at low levels everywhere and is usually regarded as safe; higher amounts, however, can be hazardous to ecosystems and human health. The effects of natural gamma radiation depend on a number of factors, such as air conditions, geological composition, and geographic location. Therefore, knowledge of the seasonal variation of natural gamma radiation is necessary for assessing potential risks and establishing appropriate mitigation measures in tandem. The aim of this research is to evaluate the effective dose rates resulting from terrestrial gamma radiation in specific areas and examine the seasonal variations in dose rates employing statistical methods. The research area comprises two valley districts of Manipur, namely Imphal east and Thoubal districts, respectively. It is noted that throughout all seasons, the effective dose rates of the areas under study follow a normal distribution for all seasons. The effective dosage rate exhibits seasonal variation, with the highest values recorded in the summer (May and June), winter (December–January) and rainy season (July–September). The maximum and lowest recorded gamma dose rates of Imphal east district are 0.86 ± 0.07 mSv/y during the summer and 0.78 ± 0.06 mSv/y during the rainy season. On the other hand, maximum and minimum dose rates of Thoubal are observed in the summer season (0.82± 0.11 mSv/y) and in the rainy season (0.74± 0.09 mSv/y), respectively. The terrestrial gamma radiation dose rate relationship between the two districts is poor, according to an inter district assessment of effective dose rates during a similar season.