This study was performed to examine the correlations among dog sperm viabilities evaluated by flow cytometry, by microscopic evaluation (ME), by carbo-xifluorescein diacetate and propidium iodide (CFDA/PI) and by hypoosmotic swelling (HOS) test. Semen were collected from 5 dogs ranging in age from 2 to 4 years. Each ejaculate was divided into 3 aliquots and different proportions of freeze-killed cells were added to each aliquot (1:0, 1:1 and 1:3). In the other experiment, semen was extended with Sweden extender containing 5% glycerol and equex STM paste, and frozen using liquid nitrogen vapor. Fresh and frozen-thawed dog sperm viability were assessed by flow cytometry using PI staining method. The accuracy of flow cytometry was evaluated by comparing with other classic assessments, microscopic evaluation, epifluorescence microscopic analysis using CFDA/PI, and HOS test. High correlations of sperm viabilities were found among flow cytometry, epifluorescence evaluation, HOS test (p<0.01) in fresh semen. Especially, sperm viability assessed by HOS test was highly correlated with viability by flow cytometry in all the ratios of live and dead spermatozoa, 1:0, 1:1 and 1:3 (p<0.01). The viability evaluated by ME were significantly correlated with that by flow cytometry in ratios of 1:0 and 1:3 (p<0.05) however, there was no significance in ratio of 1:1. The viability evaluated by C/p were highly correlated with that by flow cytometry in ratio of 1:0 and 1:1 (p<0.01) and significantly correlated in ratio of 1:3 (p<0.05). In frozen-thawed spermatozoa, the viability determined by HOS test was considerably correlated with that by flow cytometry (p<0.01). There was significant correlation between the viabilities by ME and by flow cytometry (p<0.05). But the viability evaluated by CFDA/PI was not correlated with viability by flow cytometry. The result from this study validate the use of flow cytometry as a precise method for assessing the viability of fresh and frozen-thawed dog spermatozoa.