The influence of uranium doping up to 2 at. % on grain size, electrical resistivity and dielectric constant of barium titanate ceramics has been investigated. The samples were prepared by the conventional ceramic technique using pure raw materials. The mixed oxides were calcined at 1100 oC. The pressed pellets were sintered at temperatures between 13001500 oC in controlled atmosphere of argon and oxygen. The electrical resistivity drastically decreased, from 109 to 103 cm, with increasing uranium content up to 1.5 at. % and increased thereafter to about 107 cm, for 2 at. % U. The dielectric constant slightly increased with increasing U-content, up to about 1 at. % U and then shows a sudden increase with about two orders of magnitude, having a sharp maximum at 1.5 at. % U, when sintered in argon atmosphere compared to only half an order of magnitude when sintered in oxygen atmosphere. The results are discussed in terms of the possible A and B sites occupied by uranium as well as the boundary layer enriched with vacancies.