African swine fever is a highly contagious fatal infectious disease of pigs with a worldwide occurrence and economic importance. Two adult large white boars from two farms in Jos North, Plateau State-Nigeria kept under intensive management system were diagnosed of African swine fever between the last week of July and the first week of August 2019 at the Veterinary Teaching Hospital University of Jos. In both cases the farmers complained of sudden deaths of pigs. At post mortem examination carcasses grossly showed splenomegaly, hemorrhagic lymphadenitis, and hepatomegaly with severe congestion. The kidneys were enlarged and had generalized petechiae and blood clot in the pelvis.The heart was moderately enlarged.On microscopy, the spleen and lymph nodes, showed severe lymphocytic depletion, haemorrhage and severe haemosiderosis. The liver was severely congested with focal coagulative necrosis of the hepatocytes. The kidneys were severely congested and showed renal tubular necrosis with few tubular protein casts. Tissue samples were confirmed to be positive for ASFV by polymerase chain reaction and phylogenetic analysis revealed that the isolate belonged to genotype-I. Sequences obtained were compared and deposited in the GenBank and were accessioned MN888693 and MN888694. Keywords: African swine fever; laboratory; diagnosis; smallholder farms; pig; Nigeria