Abstarct: In this study, by combining two immiscible fluids in a microchannel confinement and applying thermal condition, Droplet formation and fluid break-up dynamics in different flow condition has been investigated numerically. The numerical analysis was in basis of finite volume method, in which one fluid (with higher viscosity in comparison to the other fluid) is injected to another immiscible fluid in a microchannel with specific geometry. Depending on fluids properties and their flow rates, emulsification occurs and droplets formed with different sizes. Simulation results, obtained from software, were compared with published experimental results [1]. In this physic viscosity plays an important role in emulsification, so that the higher viscosity of the injected fluid is, the larger droplets are formed. In the following, effect of heat transfer on droplet sizes was studied and results has been reported. Result of this study would be helpful to choose fluids with different viscosities, producing determined sizes of droplets in different thermal condition.