This paper presents a strategy to improve fuel atomization during warm-up. Heating the fuel inside the fuel-rail plans improvement on fuel atomization. In this experiment, the heated fuel-rail system is constructed to investigate the reduction effects on the size of the fuel droplet by fuel heating. The fuel atomization is examined by measuring Sauter Mean Diameter (SMD) of the fuel droplets from the three different types (two-hole, pintle, and six-hole) of injectors based upon the returnless heated fuel-rail system. The results show that the six-hole type injector with the heated fuel provides the best fuel atomization results in terms of SMD among three different types of injectors.