Abstract: This paper describes the analytical method of uranium and thorium isotopes in manganese nodule samples. This method was successfully used in the determination of uranium and thorium of three manganese nodule samples from the Central North Pacific. Their concentrations range from 5.1 to 9.9 ppm and 17.8 to 92.1 ppm for uranium and thorium respectivelyAlso described here is a method for determination of growth rates of manganese nodules. Growth rates measured by ~(230)Th_((?)x) method for four nodules from the Central North Pacific are 0.8, 1.9, 2.9 and 4.3 mm/Ma respectively. The results are in reasonably good agreement with those found in other nodules by other investigators.