The standard method for the diagnostic of leptospirosis is the microscopic agglutination test (MAT). Nevertheless, it is time-consuming and presents risk of infection for laboratory personal. Several attempts to simplify and reduce the time, skill and expense required for serological testing were made. Rapid slide agglutination tests (RSAT) have been used nowadays as a reliable screening test for the detection of acute and recent infections by many laboratories. The purpose of that study was to evaluate a new antigen preparation for the rapid diagnoses of acute canine leptospirosis and to compare it with MAT results in clinically suspect serum samples. Two hundred and thirteen serum samples from dogs of both sexes and different ages were tested and 141 (66.2%) animals were considered as positive by MAT. The most frequent serovar was icterohaemorrhagiae, followed by canicola. RSAT results were very similar to those observed on MAT, with 139 (65.3%) reactive animals. Correlation between RSAT and MAT was positive (0.82) and significant (p < 0.01). Concordance of results was of 93.4% (199/ 213) of the animals correctly diagnosed by RSAT. Considering MAT as the standard test, sensitivity of RSAT was calculated on 94.3% (133/141) and specificity on 91.7% (66/72).