Biodiesel made from Jatropha oil by transesterification process has viscosity and other important physical properties comparable to mineral diesel hence it can be used as an alternate fuel in conventional diesel engines. It is important to investigate the spray characteristics of biodiesel because emissions from the engines are dependent on fuel atomization process and resulting fuel-air mixing. This study focuses on the Jatropha biodiesel spray investigations using Phase Doppler Interferometry (PDI) for measurement of various microscopic spray parameters such as Sauter mean diameter (SMD) and spray droplet size and velocity distributions. The spray and engine experiments were carried out for Jatropha biodiesel (JB100) and their 20% blends (JB20) with mineral diesel as baseline. Fuel injection pressure during the spray experiments was maintained at 200 bars for all tests, quite similar to small horse power agricultural engines, and the fuel injection quantity was varied. Spray experiments were conducted in ambient conditions. Engine out emission measurements were done on the same engine using similar fuel injection equipment (FIE) and measurement was done for HC, CO, NOx, and CO2. These experiments were conducted at same fuel quantity as that of spray experiments, by keeping the engine speed constant at 1500 rpm. Finally Jatropha biodiesel spray droplet size distribution was correlated to the emissions from the engine.