With the advent of lasers in the 1960s, researcher and engineers discovered a new and powerful tool to investigate natural phenomena and improve technologically critical processes. Due to recent progress in the area of high power fiber optics allowed convenient shielding and transmission of the laser light from one part of engine to the combustion chamber. Laser is emerging as a strong concept for alternative ignition in spark ignition engine. Laser ignition has potential advantages over conventional spark plug ignition. Laser ignition system is free from spark electrodes hence there is no loss of spark energy to the electrodes, which are also free from erosion effect. In addition the potential advantages of the lasers lies in its flexibility to change the ignition location. Also, multiple ignition points can be achieved rather comfortably as compared to conventional electric ignition systems using spark plugs, And many more. In this paper, advantages and disadvantages of laser and conventional spark ignition systems in the context of combustion engines are discussed, and performances of laser ignition and conventional spark ignition systems are comparatively evaluated in terms of Minimum Ignition Energy, Ignition Probability and Exhaust Emissions at similar operating conditions of the engine and graphs are plotted. And will also explain how laser ignition extends the lean flammability limit, while the spark ignition could be more favorable for rich mixture.