This study conducts play therapy focused on Mahler’s separation-individualization theory with stuttering children having a high level of anxiety due to failure in separation- individualization, aiming to verify its effectiveness on their anxiety, depression derived from the symptoms of anxiety, and ego-resiliency. Accordingly, a total of 54 sessions of play therapy were conducted once a week, and changes in their anxiety, depression, and ego-resiliency were analyzed, using the KPRC. The results of this study are as follows: It was found that the long-term play therapy based on Mahler’s separation-individualization theory was effective in reducing children’s anxiety. Second, it was found that the long-term play therapy based on Mahler’s separation-individualization theory was effective in reducing their depression. Third, it was found that the long-term play therapy based on Mahler’s separation-individualization theory was effective in improving their ego- resiliency.