The emission from combustion of fuels of internal combustion engine have been major part of the air pollutant sources. Emission regulations in developed countries are becoming very strict and trade off strategies in order to reduce pollutants and it is need to reduce to reduce the fuel consumption. Lean combustion is one of the best ways to reduce the fuel consumption. However, it produces higher NOx emission. The reasons are high combustion temperature and excess of oxygen in cylinder. In order to reduce these conditions, water injection would be used. A decrease in temperature of the combustion process leads to a drop in NOx formation in engines. The use of water injection in the combustion process can be a part of solution to the problem of pollution control and fossil fuel depletion. Water is sprayed into the cylinder or incoming fuel air mixture, this may lead to effectively reduce the intake temperature. The reduction of intake temperature allows for more aggressive ignition timing to be employed, lead to the increase of power output and improve the fuel efficiency. In this paper, it is presented about the investigated finding results of water injection in the suction stroke of single cylinder four stroke cycle S.I engine. The effects of variable water injected amount on the engine performance under variable load conditions are presented in this paper. The study involved the injection of water into the intake manifold in the suction stroke at the angle from 26° ATDC to 78° ATDC with specified injection durations with various water injected amounts with one injector type and the another injector type with the variable water injection duration 78° ATDC to 130° ATDC . According to the tested performance finding results, the injected amount of water 0.065ml inject is the most suitable water injection amount with the analysis of constant speed with variable load based on better performance. Kyi Kyi Aye | Yin Yin Tun "Investigation on the Effect of Intake Manifold Water Injection on the Performance of Single Cylinder Spark Ignition Engine" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-1 , December 2019, URL: https://www.ijtsrd.com/papers/ijtsrd29808.pdf