Effect of adding oxygenates on the performance, emission and combustion characteristics on a direct injection diesel engine fuelled with cotton seed oil (CSO) was investigated. Diethyl ether (DEE) was used as oxygenate. A single cylinder water-cooled direct injection diesel engine developing a power output of 5.2kW at 1500 rev/min was used. Quantity of oxygenate was varied from 10 % to 30 % to find the optimum blend performance. Brake thermal efficiency improves from 28 % with neat CSO to a maximum of 29.5 % with 30 % of DEE. Smoke value is 3.9 BSU with neat CSO, 3.6 BSU with 30 % of DEE and 3.4 BSU with diesel. Hydrocarbon and carbon monoxide emissions are also less with DEE. Peak pressure and maximum rate of pressure are found to be higher with DEE and CSO than neat CSO. On the whole, it is concluded that adding small quantities of oxygenates (DEE) can significantly improve the performance of a cottonseed oil fuelled diesel engine.