Objective: To evaluate the clinical efficacy and safety of decitabine in combination with lower-dose CAG regimen (G-CSF, cytarabine and aclarubicin; D-CAG regimen) in the treatment of myelodysplastic syndromes with excess blasts (MDS-EB) and acute myeloid leukemia with myelodysplasia-related changes (AML-MRC), compared to standard CAG regimen. Methods: A total of 42 patients with newly diagnosed MDS-EB and AML-MRC from May 2011 to March 2017 were included in the retrospective study. 21 cases were initially treated with G-CSF for priming, in combination with cytarabine of 10 mg/m² q12h for 14 days and aclarubicin of 20 mg/d for 4 days (CAG regimen) and the other 21 cases were initially treated with decitabine of 20 mg/m² for 5 days and lower-dose CAG regimen (cytarabine of 10 mg/m² q12h for 7 days, aclarubicin of 10 mg/d for 4 days, and G-CSF for priming (D-CAG regimen). After two cycles of induction chemotherapy, the patients who obtained complete remission(CR) received consolidation chemotherapy or hematopoietic stem cell transplantation (HSCT). Results: Among a total of 42 patients, the median age was 52.5 years (18-65 years) and 64.3% of them were male. Baseline characteristics of patients between D-CAG group and CAG group showed no significant differences. The CR for patients in D-CAG group was 81.0% (17/21), compared to 52.4% (11/21) in CAG group after 2 cycles of therapy (χ²=3.857, P=0.050). The overall response rate (ORR) for patients in D-CAG group and CAG group was 85.7% (18/21) and 76.2% (15/21) respectively, without significant difference (χ²=1.273, P=0.259). By December 2017, the median follow-up of D-CAG group and CAG group was 13(6-32) months and 15(2-36) months respectively. Finally, 10 patients in D-CAG group and 7 patients in CAG group received HSCT respectively. Except patients receiving HSCT, the median leukemia-free survival (LFS) time for patients in D-CAG group and CAG group was 18.0 (95%CI 6.6-29.4) months and 11.0 (95%CI 0-23.9) months respectively. Probabilities of 12 months LFS for D-CAG group and CAG group were (63.6±14.5)% and (50.0±13.4)% respectively, without difference (χ²=0.049, P=0.824). Except patients receiving HSCT, there were 2 deaths in D-CAG group and 7 deaths in CAG group respectively. The cumulative probabilities of 12 months OS for non-HSCT patients in D-CAG group and CAG group were (90.9±8.7)% and (61.5±13.5)% respectively, without significant difference (χ²=1.840, P=0.175). The incidences of side effects between D-CAG group and CAG group did not show significant differences (P=0.479), and the main side effects included cytopenias, pneumonia, infections of skin and soft tissues, neutropenic patients with fever, liver dysfunction. Conclusion The decitabine in combination with lower-dose CAG regimen improved CR for patients with MDS-EB and AML-MRC, and was a promising choice.