The compatibility problems of the mini car in car-to-car frontal collision and car-pedestrian accident are discussed using accident data and computer simulations.In our analysis of the accident data in Japan, the number of fatalities was investigated using the vehicle masses and classes. It was found that the cars with identical mass are most compatible since the injuries per accident are minimal and injury risks to the driver in both cars are the same. The analysis of the car class indicated that the mini car and the sports utility vehicle are the most incompatible car types, with low and high aggressivity, respectively.Our accident analysis in the present study shows that the safety of mini cars is the key point in achieving the compatibility in Japan. Computer simulations using MADYMO were carried out of crashes of mini car into a rigid wall and into a large car. It was found that either stiffening mini car with an optimized restraint system or modifying the large car with additional crush space can reduce the injury risk to the driver in the mini car.The analysis of car-pedestrian accidents in Japan shows that the mini car has higher aggressivity in relation to the pedestrian than other bonnet-type cars. Computer simulation revealed that the head velocity of the pedestrian at impact is high since the pedestrian head contacts the body of the mini car in the early phase.