Summary Orotate phosphoribosyltransferase (OPRTase, EC 2.4.2.10) and orotidine-55’-phosphate decarboxylase (ODCase, EC 4.1.1.23) activities were located predominantly in the soluble supernatant fraction of the cells of black gram seedlings. The activities of these two enzymes were not separable by ammonium sulphate fractionation and chromatography using Sephacryl S-200, DEAE-cellulose, and Hydroxylapitite. These findings support the idea that OPRTase and ODCase exist as a complex in plant cells. The conversion of orotate to UMP by the partially purified enzyme preparation required PRPP and Mg 2+ , and was stimulated by dithiothreitol. Black gram OPRTase was specific for orotate, and could not use uracil as a substrate. The Km values of OPRTase for PRPP and orotate at pH 7.2 were 1.6 μM and 4.5 μM, respectively. The pH optima for OPRTase and ODCase were 8.0 and 6.2–9.2, respectively. The conversion of orotate to UMP by plant OPRTase and ODCase was inhibited by xanthosine-5-phosphate, UMP, and UDP. Other tested purine and pyrimidine nucleotides showed little or no effect. The observed properties of OPRTase and ODCase of black gram are compared with the results from other organisms and discussed in relation to the biosynthesis and its control of plant pyrimidine nucleotide biosynthesis.