This study determines the population size, population distribution, breeding structure, frequency of sex, mating ratio, effective population size (Ne) and rate of inbreeding (_F) of native pig in Marinduque. A census of pig population was conducted in 18 randomly selected barangays in Marinduque province. Pigs were classified into genetic groups according to sex, state of growth, sexual maturity and physiological activity. The confidence interval and chi–square (_2) were used to evaluate the data. The rate of inbreeding was calculated from the relative values of effective population size. Results identified a total of 2,428 pigs belonging to four breeds. The native pigs composed the majority (58.57%) of the pig population (_s 2>_). The largest population was found in Sta. Cruz (42.48%) while Mogpog had the smallest (4.99%). The breeding population and non-breeding population were about 31.86% and 68.14%, respectively. The female breeders composed the majority (96.25%) of the breeding population. The mating ratio, Ne, and _F were 1:26, 65 and 0.77%, respectively.