This study was conducted to analyze the acquisition process for the production of special morae in Japanese by Korean learners, based on conversational speeches in the ACTFL Oral Proficiency Interview (OPI). The errors in pronouncing the special morae (/Q/: geminate consonants, /N/: syllable final nasal, /R/: long vowels) observed in the articulation by Korean learners were analyzed based on the OPI level, frequency and speech environment. The results show that, in relation to the frequency of errors, the frequency of insertion or lengthening of the special morae was higher than that of deletion or shortening, regardless of the OPI level. The most difficult special mora to learn for Koreans was found to be /R/ insertion, followed by /Q/ insertion, /R/ deletion, /N/ insertion or lengthening, /Q/ deletion and /N/ deletion in that particular order. In addition, there was no significant correlation discovered between the learners’ Japanese proficiency and their level of pronunciation of the special morae, and it was confirmed that non-speech factors such as vocabulary and grammar had an impact on the errors in pronouncing the special morae.