Motorcycles represent a substantial portion of the motorized fleet in Singapore, accounting for 19% of all motorized vehicles. They also account for more than their share of total accidents. From 1992 to 2000, motorcycles were involved in 35% of all motor vehicle accidents. Furthermore, motorcycles account for about 40% of total fatal accidents, substantially higher than other types of vehicles. For example, passenger cars, which represent 60% of the fleet, are involved in only about 36% of total fatal accidents. These figures suggest that motorcycling is more prone to fatal accidents than other vehicles. To reduce injuries of motorcycle related road crashes, better understanding is needed between the relationship of injury severity and risk factors. This study seeks to identify the contributing factors affecting crash severity with broad considerations of driver characteristics, roadway features, vehicle types, pedestrian characteristics and crash characteristics using ordered probit model. It also explores how the interaction of these factors will affect accident severity risk. The reported crash data is Singapore from 1998 to 2002 were used to illustrate the process of parameter estimation. The factors which increase the severity of motorcycle involved crashes are type of location (bend, T-junction, X-junction), time of the day (night), speed limit (70 km/hr, 80 km/hr), motorcycle cylinder capacity, area of accident (factor), race (Eurasian), Driver’s sex (male), pillion passenger. On the other hand, time trend (accident year) and seasonal effect (June, July, November) decrease the severity of crashes.