When the putative father is dead his probable genotype, essential for estimate of likelihood ratio in the diagnosis of paternity, should be deduced from his relatives. In the present paper are described the general method for such deduction of probable genotype and the derivation of the formula of likelihood ratio. 10(4) examples of the diagnosis of paternity of deceased father are examined using a Monte Carlo method and the distributions of relative frequencies of log(Y/X) are calculated for the true father and non-father. These results indicate that the present method of estimation of Y/X from relatives is quite useful for the diagnosis of paternity of a deceased putative father.