This study aimed to investigate the phenomenon of insertion of the geminate consonants in the intervocalic position by Korean learners of Japanese through an analysis of the “Database of Japanese language learners conversation.” The results showed that the Korean learners’ production of the Japanese voiceless consonants as geminates occurred between the voiced or voiceless consonants, although differences in the type of vowels were not observed. However, when the preceding vowels were a narrow vowel /i/, insertion of geminate consonants were observed to be frequent in the environment of vowel devoicing. Insertion of geminate consonants has been observed extensively regardless of the Japanese language proficiency of Korean learners. It should be noted that insertion of the geminate consonants are generated to concentrate at the production of the particular vocabulary and the te-form, ta-form, tara-form and tari-form of the verb. Therefore, these need to taught at the time of introduction of vocabulary and inflected forms of the verb as insertion of geminate consonants does not occur.