Two cases of congenital hyperostosis at a pig farm were observed and examined pathologically in Landrace piglets. Twenty two piglets from 2 litters: 10 alive piglets in a litter and 2 stillborn and 10 alive piglets in another, were born with thickened forelimbs and some of them with thickened hindlimbs too. These piglets stowed symptoms of staggering and incoordination. Only one of these piglets could be reared normally and all the others died within 3 days of age. The thickened parts of their limbs were felt firm and not well pitted by finger pressing. An apparent ossification was identified on the central regions of the cross sections of the thickened limbs, and some pale, gray and ossiferous signs were found in the peripheral soft areas. On histopathological examination of the thickened limbs, it was found that the bone trabeculae were newly proliferated in a concentric form in central regions and in a radiated form in peripheral regions. The peripheral regions of the periosteum and perichondrium of new bone were proliferated with connective tissue and the edematous muscle bundles were atrophic and degenerative. Both the sows which produced piglets of congenital hyperostosis were mated with a different boar at next breeding and farrowed normal piglets. It was concluded that the swine congenital hyperostosis in the present cases was expressed by autosomal recessive gene of first mating boar.