The purpose of this research was to study twenty – five samples in chokun tangerine soil keep from five place in Aumphor Betong Yala province for study Potassium – 40 in soil for analyze related between Potassium – 40 content and all Potassium in soil by Scintillation detector, NaI(Tl), Which use Cs – 137 and Co – 60 standard sorts. And then sorts sample evaluated gamma – ray at energy 1.46 MeV. That release from radioisotope of Potassium – 40