Barangan Merah is a potential type of banana to be developed under in vitro condition. Acclimatization is the final stage in the propagation by in vitro culture. The use of acclimatization medium from organic materials in the surrounding environment can be an alternative in acclimatization process. This study aims to obtain the optimal organic medium in acclimatization process for the growth of Barangan Merah banana seedlings resulting from in vitro culture. The planting material used plantlets from in vitro regeneration of banana cv. Barangan Merah from Tissue Culture Laboratory, Agricultural Faculty, Universitas Syiah Kuala. The experiment used the individual pot technique with the application of organic medium types, namely husk charcoal, sand, leaf litter compost, and oil palm fruit bunches compost. The results of this research showed that the highest number of seedlings that were still survive until the end of the acclimatization process was found in the husk charcoal medium (71.43%). The best seedling growth according to the increasing of leaves number, leaf size, and plant height in the acclimatization process was found in leaf litter compost medium.