The hypomethylating agent decitabine is the standard therapy for intermediate or high risk myelodysplastic syndrome (MDS).In this trial, 191 adult patients with intermediate/high risk MDS (IPSS score ≥ 0.5) randomly received decitabine using a standard regimen (20 mg/m2 /day for 5 consecutive days; n = 94) or an extended regimen with lower daily dose (12 mg/m2 /day for 8 consecutive days; n = 97) every 4 weeks, for a total of 4 cycles.The median follow-up was 14 months (range 2-36). The primary end point of overall response rate in the intent-to-treat analysis was 41.5% and 38.1% in the standard and extended dosing arms, respectively (p = 0.660). Complete remission and marrow complete remission also did not differ between the two arms. Cytopenia was the most frequent adverse event (76.4%). The median duration of neutropenia per cycle did not differ between the two arms during the first two cycles, but significantly shorter in the extended dosing arm in the third cycle (8.5 vs. 15.5 days, p = 0.049) and in the fourth cycle (8 vs. 14 days, p = 0.294).The 5-day 20-mg/m2 /day and 8-day 12-mg/m2 /day decitabine regimens have similar efficacy and safety in patients with intermediate or high risk MDS.© 2023 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.