We retrospectively investigated the prognostic factor of lenalidomide plus low-dose dexamethasone (Rd) in Japanese patients with refractory or relapsed multiple myeloma (RRMM) registered in the Kansai Myeloma Forum from January 2006 to December 2013. A total of 140 patients were analyzed. The median age was 66 years. The overall response rate was 68.6 %, including 33.1 % with a better than very good partial response. At 13.0 months median follow-up, the median overall survival (OS) and progression-free survival (PFS) were 34.2 and 17.0 months, respectively. In univariate analyses, patients with one or two prior therapies had significantly longer OS (41.2 vs. 21.5 months; P = 0.002) and PFS (29.0 vs. 13.0 months; P = 0.006) than patients treated with three or more prior therapies. Prior use of thalidomide was associated with significantly shorter PFS (19.0 vs. 16.0 months; P = 0.045). The prior use of bortezomib or high-dose therapy with stem cell transplantation, and the International Staging System had no impact on long-term outcome. Multivariate analysis showed that only the number of prior therapies was a significant predictor of both OS and PFS. Our findings suggest that greater benefit may occur when Rd therapy is used at the first or second relapse in RRMM.