The employment of asymmetric decentralization to deal with separatist conflicts has become increasingly popular in recent years. However, contentions remain as to whether it is an effective tool to deal with separatist conflict. This article extends the debate by looking specifically at the conditions that affect the effectiveness of decentralization. It argues that the workability of decentralization in dealing with separatist conflicts is affected by the degree of accommodation in both the process of designing the policy and the policy outcomes it succeeds in bringing. It pursues this argument qualitatively by using the cases of Aceh and Papua in Indonesia. Decentralization successfully tamed the separatist conflict in Aceh because it involved separatist elements in designing the plan and succeeded in achieving most of the promised outcomes. In contrast, decentralization failed to tame separatist demands in Papua because It enabled only limited participation of separatist elements in the design process and brought only limited outcomes.