Biodiesel production with 6/2 pulsed ultrasonic single and dual frequencies were conducted under M/O molar ratio (9:1), CaO catalyst (size 200 mesh at 8%wt), time (37 min), intensity (0.91 W/cm(2)). Powers of waves were 140 W for single waves, and 70W + 70W for dual case. Biodiesel yield for dual frequency case was 96.16% while those of single 28 kHz and 40 kHz cases were 94.42% and 93.60% respectively. The power ratios were varied for the dual cases at 0/140, 20/120, 40/100, 60/80, 70/70, 80/60, 100/40, 120/20 and 140/0 W. The highest yield of 97.13% was obtained at 120/20 W. It was found that lower frequency waves played more important role than higher frequency. Thus, 28 kHz was used as the resonance frequency to determine the resonance size of the catalyst (equal to 49.50 mu m). Lastly, biodiesel productions were conducted with 6/2 pulsed dual frequency waves (28 + 40 kHz, 120/20 W) and varying catalyst size as 150, 74, 38, 25 and 18 mu m. The 38 mu m size gave highest yield of 98.85% due to it was closer to the resonance size compared to the others. Thus using pulsed dual waves with optimal catalyst size can enhance the production yield from 93.60% to 98.85%. (C) 2020 Elsevier Ltd. All rights reserved.