Many radioactive elements have existed when the Earth had appeared and the long living of them are still present. One of the most important of these radioactive elements is K-40. It makes about 0.012% of total content of K, widely represented in many different rocks. In this study the distribution of the natural K-40 radioelement in the volcanics of the south part of Afyon was investigated. Gamma-ray spectrometer was used for in-situ measurements of this radioelement concentration. Studied area has covered approximately 1800 km(2). In-situ measurements were performed at 1390 different locations in this field. Data for each measurement was gathered during 3 min. The map of the K-40 element distribution in the studied area was produced. The high values of K-40, according to this map, were obtained in the areas of the alteration zones, between Sandikh and Suhut in the studied area.