This study was carried out to assess the feasibility of ultrasonographic measurements of the optic nerve sheath diameter (ONSD) in normal dogs and evaluate the effect of breed, sex, body weight and age on biometry of ONSD. The ONSDs were evaluated in 15 dogs (10-50 months old) with normal eye (7 Yorkshire terrier and 8 Maltese). Ultrasonographic measurements of the ONSD were carried out at a constant position located 5 mm behind the optic disc. Eyes were collected immediately after euthanasia, and were used for saline immersion technique and direct measurement by calipers for biometry of ONSD. In this study, there was no significant difference of ONSD between the left and the right eyes, and was no significant difference among ONSD values obtained from ultrasonographical method, saline immersion technique and direct measurement (k=0.95). Also, there was no correlations between ONSD and sex, body weight and age, but was significant between the mean ONSD of Yorkshire terrier and Maltese (p<0.01). The mean ONSD of Yorkshire terrier was 2.10 +/- 0.22 mm and Maltese was 1.63 +/- 0.23 mm. This study suggests that ultrasonographic measurements is useful method for biometry of the ONSD in normal dogs and provides baseline information for the study of evaluating ONSD in various breeds and diagnosing several diseases with the change of the ONSD.