Diesel engines are very efficient prime movers in their power range. Fuel is directly injected into the combustion chamber. Performance and emission characteristics of diesel engines are highly influenced by the fuel spray parameters and atomization of the injected fuel. As the emission regulations become stringent, it is very important to optimize the combustion in internal combustion engines for different fuels including alternative fuels. Spray visualization using optical techniques play a very important role to analyze macroscopic spray parameters and fuel atomization behavior. In the present experimental study, an important alternative CI engine fuel, Karanja oil and its blends with diesel have been investigated for their spray parameters and fuel atomization relative to mineral diesel. These parameters are different for the two fuels because of difference in the viscosity and density of the fuels. Combustion chamber pressure is a dominant factor, which strongly influences the spray characteristics. This research is a comparative study of the effect of ambient pressure on macroscopic spray parameters such as spray tip penetration, spray cone angle and spray area, of mineral diesel, Karanja oil (K100) and blends (K5, K20). Experiments were carried out in a constant volume spray visualization chamber under different chamber filling pressure (1, 4, 7 and 9 bars) at a fuel injection pressure of 200 bars. The light intensity on the illuminated spray was analyzed to find the atomization level of different fuels. Spray parameter like spray tip penetration, cone angle and the spray area were found to be higher for Karanja oil (K100) as compared to blends (K20 and K5) and mineral diesel. It was observed that as the concentration of Karanja oil in the blend decreases, atomization actually improves. It was also found that with increasing chamber pressure, atomization of fuel becomes relatively superior.