This work discusses the utilization of flyash for synthesis of heterogeneous catalyst for transesterification. Different types of zeolites were synthesized from alkali fusion followed by hydrothermal treatment of coal flyash as source material. The synthesis conditions were optimized to obtain highly crystalline zeolite based on degree of crystallinity and cation exchange capacity (CEC). The effect of CEC, acid treatment, Si/Al ratio and calcination temperature (800, 900 and 1000 degrees C) on zeolite formation was also studied. Pure, single phase and highly crystalline zeolite was obtained at flyash/NaOH ratio (1:1.2), fusion temperature (550 degrees C), fusion time (1 h), hydrothermal temperature (110 degrees C) and hydrothermal time (12 h). The synthesized zeolite was ion-exchanged with potassium and was used as catalyst for transesterification of mustard oil to obtain a maximum conversion of 84.6% with 5 wt% catalyst concentration, 12:1 methanol to oil molar ratio, reaction time of 7 h at 65 degrees C. The catalyst was reused for 3 times with marginal reduction in activity. (C) 2015 Elsevier B.V. All rights reserved.