Banana bark is organic waste which has nutrients that are useful for plants. This study aims to determine the effectiveness of liquid organic fertilizer (LOF) of banana bark as a potassium source for growth and yield of purple eggplant, and determine the right balance of the use of potassium sources from organic liquid fertilizer banana peel and KCl fertilizer. The study was conducted at the UMY Agricultural Experiment Field with the implementation period from September to November 2018. The study was conducted using a Completely Randomized Design (CRD) wich consist of 6 treatment levels are : 100% K (LOF banana bark), 80 % K (LOF banana bark) + 20% K (KCl fertilizer), 60% K (LOF banana bark)+ 40% K (KCl fertilizer), 40% K (LOF banana bark) + 60% K (KCl fertilize)r, 20% K (LOF banana bark) + 80% K (KCl fertilizer), and 100% K (KCl fertilizer) as control. The results showed that the comparison of banana peel liquid organic fertilizer treatment gave similar results to the growth and yield of purple eggplant.