Laboratory diagnosis of brucellosis is made by serological, molecular or cultural methods. Brucella spp., Agrobacterium, Ochrobactrum and Rhizobium all belong to the alpha-2 subgroup of Proteobacteria as revealed by studies on 16S rRNA sceqence analysis. O.anthropi has been used to diagnose brucellosis. In this study, whole cell extract from Rhizobium tropici (R. tropici) was examined for detecting antibodies to B. abortus and B. melitensis in cattle and sheep sera (200 in total), respectively. Genetic similarity between the bacteria R. tropici, B. abortus and B. melitensis was also investigated by RAPD-PCR. Using the sera from cattle, sensitivity and specificity were calculated as being 81.1% and 22.6%, respecitively when the SAT considered as Gold Standard. RLAT's sensitivity for sheep sera (80.1%) was found being close to that of cattle sera (81.1%) while specivity of RLAT for sheep sera (59.5%) was quite higher than the figure for the cattle sera (22.6%). In conclusion, use of whole cell antigen from R. tropici is not practical in sero diagnosing brucellosis in cattle and sheep. It is also considered that some antibodies to R. tropici are also mounted in the hosts contributing misunderstanding of the positivitiness in the serology.