The study of natural radionuclide materials is important to assess the health hazards on human being and one of these materials is 40 K which is present in soil and different types of stones. This study is performed to assess the 40 K concentration in mudstones in the north of Iraq by (flame photometry and γ-ray spectroscopy) and to compare between these two techniques in measuring its level. So the activity of potassium was measured by these methods, and their results were compared with the results of other studies. The results show that the concentration of 40 K ranges from 284.3 Bq/kg to 2481.2 Bq/kg using γ-ray spectroscopy and 511.7 Bq/kg to 3623.6 Bq/kg using flame photometer technique and these results were comparable with the upper level of the world mean specific concentration of 40 K and cause no health hazard. The results obtained by the two methods were also, compared using T-test and P-value and they show no statistical significant difference.