In this study, we carried out grammaticality judgment test of ‘ey, eyseo, ro’ adverb case markers in Korean, with 60 Lao Korean learners from sophomore to seniors majoring in Korean language in Lao National University(20 learners in each year), with the comparison group consisting of 39 Korean native speakers, in order to figure out acquisition aspects. To meet the goal, this study developed a grammaticality judgment test with 156 sentences. In the results of the study, (1) Lao Korean learners showed low accuracy rates and meaningful difference with Korean native speakers. (2) Lao learners showed high accuracy rates in ‘direction(71.83%)’ and ‘time(71.83%)’ among four usages of ‘ey’, ‘background(68%) among three usages of ‘eyseo’, ‘tools and means(84.17%)‘ of (e)ro’, whereas they showed the lowest accuracy rate(63.67%) in ‘departure and starting point’ among four usages of ‘eyseo’. (3) The difference of accuracy rates among sophomores, juniors and seniors was examined. As their grades gets higher, no significant improvement was seen in the grammaticality judgment of three adverb case markers; however, the only significant discrepancy was found between sophomores and seniors. These results proved that instructional intervention is still necessary.