This study focused on the acquisition of dative alternation by a Japanese English learner through a qualitative research using protocol analysis. From the results of the quantitative research carried out by Sakamoto(2001a, b), it was found that the learners' L1 (i.e., Japanese) partially influenced their interlanguage and also that their knowledge of dativizability was different among the verb classes. However, the exact procedures of how the learners judge the dativizability of verbs in those studies remained unclear. This study sought to further clarify these procedures, and also tried to determine what kinds of factors affect when learners judge the dativizability of each verb. The findings of this qualitative research confirmed the results and findings of the previous studies; moreover, it provided evidence on the procedures involved in how the learner created a sentence which included a dative verb.