Recently, a long distance Inter City Bus Network has been developed in Japan. The maxi mum traveling distance is approximately 1,000 km. The driver and passengers must endure long periods of sitting in the same seat. Therefore, the ride comfort ability is the most important characteristic for the Inter City Bus. Noise and vibration level have the greatest effect on ride comfort, therefore they must be considerably reduced to realize the good comfortability.This paper presents the methods of analysis and improvement to reduce the bus body vibration excited by road surface roughness. Modal Analysis Method and Finite Element Method are applied to the bus body construction. Further more, the relationship between the bus body vibration and engine suspension system characteristics are investigated. These analyses and investigations make clear that the bending vibration of the bus body and the damping factor of the engine mount system are the main causes of bus body vibration excited by road surface roughness.Using the results from these methods of analysis the Inter City Buses natural frequency is altered so as to improve the ride comfort ability.