The thirst for fuel is steadily increasing as technology continues to open new areas of exploration. At the same time, the indiscriminate extraction of fossil fuels may also result in pollutant emissions which cause major impacts on ecological systems. In order to overcome the above problems, a suitable biodiesel should be used to replace the diesel fuel. Hence, in this work, feasibility of using biodiesel prepared from fish oil was investigated. Experimental tests were carried out to evaluate the performance, emission and combustion characteristics of a single cylinder, constant speed engine using several blends under variable load conditions. It was found that NOx, HC and CO emission was reduced for blends along with a marginal increase of brake thermal efficiency and smoke. The ignition delay and maximum heat release rate were reduced compared to diesel. Ultimately, fish oil can indeed become the appropriate source for biodiesel with environmental benefits. © 2013 Inderscience Enterprises Ltd.