The results of this study show that waste fish oil from fishmeal plant has a good potential to be used as a biodiesel source. Lower cost of the feedstock and reaching higher methyl ester content in biodiesel production at shorter reaction times is comparable with vegetable oils. Study on the FFA content has shown that low amount of FFA could effect on the yield of reaction and exact pre-treatment could minimize the saponification and produces higher yields. Investigation on the effect of temperature, methanol to oil molar ratios and catalyst loading on the biodiesel production with ultrasonic and conventional methods show that 30 min ultrasonic has higher yield than one hour in the conventional method. The results show that 87% of methyl ester and 79.86% yield can be obtained at optimum conditions of temperature 55 °C, catalyst loading of 1 wt.%, 6:1 molar ratio.