This paper explores the feasibility of converting waste Rohu fish (Labeo rohita) scale into a high-performance, reusable, low-cost heterogeneous catalyst for synthesis of biodiesel from soybean oil. The thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) analysis revealed that a significant portion of the main component of fish scale i.e. HAP (hydroxyapatite) could be transformed into beta-tri-calcium phosphate when calcined above 900 degrees C for 2 h. Scanning Electron Microscopy (SEM) morphology studies of the calcined scale depicted a fibrous layer of porous structure; while a BET surface area of 39 m(2)/g was measured. Response surface methodology (RSM) was employed to determine the optimal parametric conditions viz, methanol/oil molar ratio, 6.27:1, calcination temperature, 997.42 degrees C and catalyst concentration, 1.01 wt.% of oil corresponding to a maximum FAME yield of 97.73%. Reusability results confirmed that the prepared catalyst could be reemployed up to six times, procreating a potentially applicable avenue in biodiesel synthesis. (C) 2010 Elsevier Ltd. All rights reserved.