Aims: To assess the efficiency of a single antigen for the complement fixation (CF) test, prepared by combining Brucella abortus smooth strain 99 (S99) with Brucella abortus rough strain RB51( RB51), in detecting cattle and sheep infected or vaccinated with Brucella spp. Methods and Results: Serum samples from B. abortus-infected and RB51-vaccinated cattle were tested by the CF test using S99, RB51 and the combined S99 RB51 as antigens. Likewise, serum samples from Brucella melitensis-infected, RB51-vaccinated and Brucella ovis-infected sheep were tested by the CF test using S99, RB51, hot saline (HS) and combined S99 RB51 as antigens. Comparative analysis of the CF results showed that no reduction of sensitivity or specificity occurs when S99 RB51 antigen is used instead of specific antigens used separately. Conclusions: The results of this study indicated that combined S99 RB51 antigen used in the CF test, because of its specificity and sensitivity, could be used in animal brucellosis surveillance systems to improve the efficiency of the preliminary screening of herds. Significance and Impact of the Study: This study proposes an improved antigen for the CF test for the epidemiological survey of animal brucellosis. It could represent advantages over standard protocols because of its ability to detect antibody responses following infection or vaccination with Brucella strains of rough and smooth phenotype.