In this paper, an experimental study was performed to investigate characteristics of flame propagation and knocking combustion of hydrous (10% water content) and anhydrous ethanol fuels with different air/fuel ratios in comparison to the RON95 gasoline. Experiments were conducted in a full bore overhead optical access single cylinder port-fuel injection spark-ignition research engine. High speed images of total chemiluminescence and OH emission was recorded together with the in-cylinder pressure, from which the heat release data were derived. The results show that under stoichiometric condition anhydrous ethanol and wet ethanol with 10% water generated higher IMEP with slightly retarded MBT spark timing than the gasoline fuel for a fixed throttle position. Under rich and stoichiometric conditions, the knock limited spark timing was limited to 35 obTDC at 1200rpm and 5 bar of IMEP when both ethanol and E90W10 were free from knocking combustion. Heat release analysis reveals ethanol had the highest maximum cylinder pressure at the earliest crank angle, followed by E90W10 and then gasoline, because of their relative earlier combustion phasing (CA10 and CA50) and short combustion duration. This is confirmed by the faster developing flame fronts of ethanol fuels shown by the high speed combustion and OH images. The difference in the flame radius among anhydrous, hydrous ethanol fuels and gasoline tends to decrease when a fuel lean mixture is used. With the rich fuel/air mixture, the flame’s edges of all fuels are more wrinkled compared with that of stoichiometric and lean condition.