[en] Natural radioisotopes contained in foods can enter the human body by ingestion and contribute to internal doses to the population. It is necessary to measure the concentration of natural radioisotopes especially thorium in Korean foods and estimate the internal doses. In this study, we have established the thorium measuring process based on the thorium extraction chemical process and alpha spectroscopic method. The concentration of Th-228, Th-230 and Th-232 in Korean vegetables (potato, sweet potato, radish, cabbage, hot pepper, garlic, onion and pumpkin) and fruits(apple, persimmon, orange, pear, grape) are measured and their internal doses are estimated