This study investigates the cycle performance and potential advantages of the replacement of fin-and-tube evaporator with parallel flow micro-channel evaporator, in R134a roof-top bus air conditioner system. The heat exchanger for the bus system are featured by a stringent space height limitation. Based on the space requirement, micro-channel evaporator with horizontal configuration and vertical configuration are both designed and manufactured. 4 or 6 piece micro-channel evaporators are parallel installed in an 8 m bus air conditioner, instead of the original two piece fin-and-tube evaporators. Additionally, each evaporator employs a single thermostatic expansive valve (TXV) to control outlet superheat, which aims to cope with the problem of refrigerant mal-distribution among multi micro-channel evaporators. Except the replacement of evaporator, TXV and the adjustment of connecting pipe, other cycle components are kept same. Experiments were carried out to evaluate the cycle performance of using micro-channel evaporator in roof-top bus air conditioner. The cooling capacity, system coefficient of performance (COP) and R134a refrigerant charge are compared between micro-channel evaporator system and fin-and-tube evaporator system in standard cooling condition. Potential advantages including cost saving, automotive lightweight and compact installation were also discussed for the application of micro-channel evaporator in roof-top bus air conditioner.