The aim of the present study is to determine experimentally the effects of ethanol fumigation (EF) on the performance parameters and NOx emission of a naturally aspirated pre-chamber diesel engine and also to compare the EF results to that of turbocharged diesel engine. By this way, it has also been indented to determine whether or not EF gives power increment at the level of turbocharging. The engine which was originally turbocharged has been converted to naturally aspirated diesel engine by dismantling its turbocharging system. Here, ethanol was introduced into the intake air by a carburetor, which main nozzle section is adjustable to give approximately (2, 4, 6, 8, 10 and 12) % (by vol.) ratios. Experiments were performed at two diesel fuel delivery rates (FDRs), six different engine speeds for six different ethanol fumigation ratios (EFRs). Variations of performance parameters and NOx emission for these six ethanol percentages in respect to neat diesel fuel (NDF) were determined and compared. It was determined that for 1/1 FDR, similar to(7.5-11) % ethanol addition into the intake manifold reduces NOx emission and improves engine performance for this engine. But, fuel cost for (7.5-11) % ethanol addition is expensive. For 3/4 FDR; similar to(7.5-12) % ethanol fumigation can be applied at (1500-3000) rpms in this engine and for these conditions NOx emission and bsfc decrease simultaneously without any significant effective power penalty. Also, it was concluded that EF improves engine performance parameters and NOx emission but does not increase effective power at the level of turbocharged version.