Finless porpoise, Neophocaena asiaeorientalis sunameri, inhabits coastal waters in East Asia and is exposed to various human activities. Abundance of the Inland Sea population in Japan is known to have reduced dramatically. Although the human-induced mortality can be a threat to the population, its future effects have not been evaluated for deficiency of demographic information. In order to make appropriate conservation actions before the population size decreases to a critical level, the adequate future projections are needed. In this study we tried a Population Viability Analysis for the Inland Sea population with a Leslie matrix model composed of the age-specific survival and fertility rates. We randomly sampled values of survival rates from the estimates of other cetaceans with similar life histories to describe the uncertainty in the annual rate of increase λ. Combining the estimates of λ with the possible human-induced mortality rates M and the abundance estimate, future population changes and extinction probability were predicted. The extinction probability after 100 years exceeded 10% at plausible ranges of λ and M. Our results suggested even a little effort for reducing the human-induced mortality is effective for persistence of the population.