Rumen fluids were collected from a slaughterhouse. Mixed rumen contents of sheep and Holstein cows were transported to the laboratory in thermos flasks, separately for each species. Ammonium sulphate and acetone were used for precipitation of protein in cell free rumen fluid. The precipitate that was observed after freezing and thawing of cell free rumen fluid and precipitate, obtained with 25% saturated ammonium sulphate showed no urease activity. Urease activity in precipitates from 80% saturated ammonium sulphate for cows and sheep were 3.6l and 6.17 (microgram ammoniaN, mg^–1 protein. min^–1), respectively. These amounts for acetone precipitate for cow and sheep were 1.88 and 0.48, respectively. Sodium dodecyl sulphate (SDS) acrylamide gel electrophoresis indicated the same subunit urease enzyme for sheep and cow. The molecular weight of rumen urease subunit was estimated to 75000 daltons, which is less than jack-bean urease (96000 daltons). Native urease did not separated by 3.2% acrylamide gel electrophoresis. The latter finding may indicate that rumen urease has a hexameric structure with more than 1500 kilodaltons.