The visual, proprioceptive and vestibular systems are necessary to maintain the body balance. Among them the pathways of visual and vestibular system are complex from end organ to posterior fossa. Analysis of ocular movement for visuo-ocular reflex and vestibulo-ocular reflex are necessary to obtain diagnosis of lesions in posterior fossa. Optokinetic after-nystagmus(OKAN) appears after abrupt cessation of optokinetic stimulation and is a available test for detecting the site of lesion of central nervous system in dizzy patient. But its normal value has not been reported in the literature of our country. Authors performed OKAN test in 40 normal adults(80 sides), aged from 24 years to 32, using Ohm-type stimulator. We divided the subjects into two groups, one consisted of 20 subjects(40 sides) who were stimulated with the acceleration of 1°/sec², the other of 3°/sec². The results were obtained as follows : 1) In ""pre-test"", the speed of effective maximal stimulus in the group of 1°/sec² optokinetic stimulation(OKS) was 61~105(mean 76.5)°/sec and that in group of 3°/sec² was 81~150(mean 119.2)°/sec. 2) The response with eye open in darkness was better than that with eye close. 3) In the group of 1°/sec² OKS, phase Ⅰ of OKAN was revealed in 95.0%, and phase Ⅱ was revealed in 5.0%. In the group of 3°/sec² OKS, phase Ⅰ was revealed in 82.5%, and phase Ⅱ and III were revealed in 12.5% and 5.0% respectively. Phase Ⅱ and Ⅲ were reveal more commonly in the group of 3°/sec² OKS. 4) In the sides of OKAN appearing phase Ⅰonly among the group of 1°/sec² OKS, duration, number of OKAN and average slow phase velocity were 24.3±13.5sec, 19.6±11.5 beats and 7.2±3.9°/sec. In the sides of OKAN appearing phase Ⅰ only among the group of 3°/sec² OKS, duration, number of OKAN and average slow phase velocity were 24.0±11.4 sec, 12.6±7.0 beats and 7.3±4.1°/sec. Their Rt-Lt differences were least in average slow phase velovity(p<0.01) in both group. 5) In the sides of OKAN appearing both phase Ⅰ and Ⅱ among the group of 3°/sec² OKS, the sum of phase Ⅰ and Ⅱ of the duration, number of nystagmus and average slow phase velocity were 17.9±12.2 sec, 36.8±23.5 beats, 6.0±3.4°/sec, and revealed phase Ⅰ only in its opposite sides. The duration in the side revealed phase Ⅰ and Ⅱ was longer than in opposite side of phase Ⅰ only, but was not significant statistically(p>0.01). 6) In the view point of regression pattern on time of OKAN by 3°/sec² OKS considered in 3-seconds interval of the phase Ⅰ and Ⅱ, the number of OKAN, slow phase velocity of first OKAN and average slow phase velocity were similar.