The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, which measures the reduction of MTT, is commonly used to validate the viability of metabolically active cells. This study was conducted to evaluate and validate the MTT assay to assess the spermatozoal viability of Nili-Ravi buffalo bulls and compare the efficiency of the test with the supravital staining technique (eosin and nigrosin) and the hypoosmotic swelling test. Fresh semen samples from breeding Nili-Ravi buffalo bulls (n = 25) were collected using an artificial vagina. After assessing the quality of the semen for routine variables, the MTT assay was carried out in PBS. Results revealed a correlation (r = 0.979; P < 0.001) between the viability of spermatozoa and the rate of reduction of MTT. The other proportions of same semen samples showed a poor relationship between the eosin and nigrosin test (r = -0.25), the hypoosmotic swelling test (r = -0.12), and motility (r = -0.15). However, the MTT assay was found to be superior compared with other tests because it was able to determine those spermatozoa that were more than 90% viable. In conclusion, the MTT assay is a simple, robust test that can be used to select Nili-Ravi buffalo bulls on the basis of spermatozoa quality.