Research on Tohoku dialects, which is a variety of Japanese, has found that the voiceless stops /k/ and /t/ in the intervocalic position are frequently realized as voiced stops. However, the phenomenon has mainly been judged aurally in the Japanese linguistics literature and has not been confirmed by acoustic measurements. We measured the VOT of data originally collected in the survey of Tohoku dialects by [1]. The data used in this study includes two age groups from eight sites. The results demonstrate that for word medial stops, the VOT distribution of voiced and voiceless stops largely overlapped, while, the laryngeal contrast was maintained for the word initial stops. Intervocalic voicing neutralization was confirmed by quantitative acoustic measurements. The effects of neighboring vowels were also investigated to show that height, but not duration, had a significant effect on voicing neutralization. Our results shed light on the phonetic nature of Tohoku dialects as well as on their phonological structure, such as the role of voicing contrast.