This study aimed to explore base catalysts with high transesterification efficiency to be used for heterogeneous biodiesel production. Cinder, a solid waste from coal burning industry, with 0.9-2.0 mm diameter, served as the support for CaO/KF to prepare base catalyst particle. The catalyst was characterized by base strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET) surface area, and the triglyceride (TG) conversions were determined using high performance liquid chromatography (HPLC). The effects of various parameters such as catalyst loading, molar ratio of methanol to oil and reaction time on the activity of catalyst were determined. The reusability and stability of the catalyst were investigated. Results showed that a maximum TG conversion of 99.9% catalyzed by 2.1% catalyst (based on the weight of soybean oil) in 20 min was obtained with methanol/oil molar ratio of 12:1. TG conversions were from 99.9% to 96.6% from the first to the fourth time use of the catalyst particle. The formed KCaF3 and K2O were the main active components for the catalyst activity. The leakage of K and Ca to the water and methanol and the occupation of the active sites by oleic acid were the main reasons for the decrease of TG conversion during repeated use of the catalyst. Fluoride leached into soybean oil, oleic acid, water, and biodiesel were negligible. However, about 3.0 and 1.5 mg F were dissolved into methanol and glycerol. It should be considered in the processes of recycling methanol and purifying glycerol. (C) 2012 Elsevier Ltd. All rights reserved.