Abstract The presence of naturally occurring radionuclides is common in all living and non-living frameworks, which are part of our environment. The activity concentration of 40K radionuclide was estimated using gamma spectrometry in some medicinal plants and transfer factors (TF), and Average Annual Committed Effective Dose (AACED) was evaluated. The standard methods were followed in the process of sample collection and processing. The mean activity concentrations of 40K were 223 and 1330 Bq kg−1 in soil and medicinal plants, respectively. The mean TF and AACED were found to be 6.5 and 8.2 μ Sv y−1, respectively. Higher activity concentration was observed in some medicinal plants due to the selective and preferential uptake of this radionuclide depending on their medicinal utility. The study may help to form the database and safety regulations connected with 40K activity in medicinal plants.