The use of OH-impregnated CaO as heterogeneous catalyst in the conversion of refined coconut oil into crude biodiesel was investigated in this study. Wet impregnation method was used to study the effects of NaOH concentration (10-20% (w/v) solution), calcination temperature (550 degrees C-70 0 degrees C), and calcination time (2-5.5 h). Characterization of the OH-impregnated CaO catalyst was done using XRD, FTIR, and SEM. Conversion of refined coconut oil into biodiesel was performed via transesterification with methanol at 60 degrees C using OH-impregnated CaO as catalyst. Results show that a 66.36% conversion to biodiesel can be achieved in 10 min when 20% (w/v) NaOH solution was used during impregnation with calcination at 600 degrees C for 2 h. Addition of tetrahydrofuran as cosolvent increased the conversion further to 81.70% which is comparable to the 85.98% achieved when using NaOH as a catalyst under the same reaction conditions. (C) 2020 Elsevier Ltd. All rights reserved.