Phase II trial combining azacitidine with valproic acid as maintenance therapy post allogeneic stem cell transplantation in patients with high-risk MDS/AML. We hypothesize that adding valproic acid to azacitidine will improve outcomes via both direct anti-tumor and immunologically mediated antitumor response with alloreactive donor lymphocytes, having an additive effect and extending 1 year survival in patient with high-risk AML/MDS after hematopoietic stem cell transplant. Based on aforementioned data from the US Department of Health and Human Services, standard 1 year survival for AML after stem cell transplant is near 40%. We hypothesize that valproic acid and azacitidine will prolong survival, with a 1 year survival goal of 60%. In addition to assessing for 1 year survival, we will have secondary objectives of assessing progression-free survival, relapse, and toxicity. The primary toxicity endpoint from this will be cytopenias and infections.