Background: Goshajinkigan (GJG) is used for the treatment of several neurological symptoms. We investigatedthe efficacy of GJG and mecobalamin (B12) against neurotoxicity associated with docetaxel (DOC) in breastcancer patients. Materials and Methods: Sixty breast cancer patients were treated with DOC. Thirty-threepatients (GJG group) received oral administration of 7.5 g/day GJG and 27 patients (B12 group) received oraladministration of 1500 μg/day B12. Neuropathy was evaluated according to DEB-NTC (Neurotoxicity Criteriaof Debiopharm), Common Terminology Criteria for Adverse Events (NCI-CTC) ver. 3.0, and a visual analoguescale (VAS). This study employed a randomized open design. Results: The incidence of neuropathy was 39.3%in the GJG group, and 88.9% in the B12 group (p<0.01). In the GJG group, grade 1 DEB-NTC was observedin 2 cases, grade 2 in 5 cases and grade 3 in 5 cases. Grade 1 NCI-CTC was observed in 7 cases, grade 2 in 6cases, and VAS was 2.7±2.2. In the B12 group, grades 1, 2 and 3 DEB-NTC were observed in one case, 12 casesand 12 cases, respectively; and grades 1, 2 and 3 NCI-CTC were observed in 11 cases, 12 cases and one case,and VAS was 4.9±2.4. Conclusions: Concomitant administration of GJG is useful in preventing neuropathy inbreast cancer patients treated with a DOC regimen.