Recently, the influence of phonological information in visual word recognition has attracted a great amount of studies. Especially, languages with a clear syllable boundary, such as Spanish and French, have reported the syllable-based sub-lexical unit in visual word recognition. The present study investigated whether sub-lexical unit in Korean visual word recognition is phonological syllable or orthographic syllable. In Experiment 1, we orthogonally manipulated the number of phonological syllable neighbors and the number of orthographic syllable neighbors in Korean disyllable words and conducted a lexical decision task. In Experiment 2, new words were used in a computational simulation. The results of two experiments showed the inhibitory effect as increasing the number of phonological syllable neighbor. We can account that the inhibitory effect is due to the lexical competition between phonological syllable-based candidates in the lexical level. The present study expands the notion that the syllable is an important sub-lexical unit in visual word recognition and also phonological information is a main function of lexical process.