In the present study, the effects of ammonia fumigation on the engine performance and exhaust emissions have been investigated experimentaly in a small diesel engine. Experiments have been performed for (2, 4, 6, 8, 10)% (by vol.) ammonia ratios at different engine speeds and loads. Here, 25% ammonia solution (25% ammonia + 75% water) have been used and this solution has been injected into intake air by a carburetor, which main nozzle section is adjustable. The test results showed that brake specific fuel consumption (bscf) increases at 2000 and 3000 rpms, but it decreases at 2600 rpm. The maximum reduction of bsfc has been determined as 7.28% for 5.48% ammonia ratio at 2600 rpm. Effective efficiency increases at all of the selected engine speeds and loads. However, the increase ratios of effective efficiency at 2600 rpm are higher than that of the other engine speeds. Exhaust emissions have been measured at 2200 rpm for different ammonia ratios and different loads and at 2600 rpm for different ammonia ratios, under only 6 Nm loads. It has been determined that carbon dioxide generally reduces at selected two engine speeds. However, nitrogen oxides, hydrocarbons and carbon monoxide generally increase. Total fuel cost for applied different ammonia ratios becomes lower than that of neat diesel fuel at 2600 rpm. At the other selected engine speeds; although total fuel cost decreases for some working conditions, it increases in some operating conditions. The maximum reduction of total fuel cost has been determined as 8.87% for 5.48% ammonia ratio at 2600 rpm.