This study investigates changes in Tōhoku dialect speakers’ phonology after their immigration to Hawaii, specifically concerning intervocalic voicing and alveolar/palatal mergers. Tōhoku dialect is known for its unique phonology compared to other Japanese dialects and, for this reason, it is often stigmatized. Previous studies of second dialect acquisition have suggested that older speakers tend to retain the phonological features of their original dialects during dialect contact situations. The results from adult Japanese plantation immigrants, as expected, suggested that adult Tōhoku dialect speakers demonstrated limitations in acquiring second dialect phonology in their contact with non-Tōhoku dialect speakers. However, there are different degrees of second dialect acquisition between the intervocalic voicing and alveolar/palatal mergers among the Tōhoku dialect immigrants who interacted with non-Tōhoku dialect speakers on a daily basis and those who did not; namely, the former eliminated the stereotypical stigmatized Tōhoku dialect feature – the mergers – more than those speakers who did not have such frequent interaction. This suggests that both sociolinguistic factors, e.g., dialect discrimination by peers, as well as relative phonological complexity, influence the rates of second dialect acquisition.