The main objective of this research work is to evaluate the Nitrogen oxide (NOx) Emission of compression ignition engine using nano-particles as constituent of jatropha biodiesel and diesel. In order to evaluate the effect of nano-paritcles such as cobalt oxide and iron oxide fuelled with diesel and jatropha biodiesel, an experimental investigation was carried out to study the emission characteristics of single cylinder, four stroke, water cooled compression ignition engine. Cobalt and Iron oxide nano-particles were added with jatropha biodiesel and diesel in different mixed proportions. The range of nano-particles size was 30-100 nanometers. The result showed reduction in Nitrogen oxide (NOx) Emission.