Understanding of interface electronic property of organic/organic heterostructures is one of the important issues for the development of organic electronics. Herein, we report the visualization of both morphology and interface potential profile of two similar organic/organic heterostructures using Kelvin probe force microscopy. Both heterostructures adopt pentacene molecules as the top layer and using two conjugate oligomers as the bottom layer. Although they show similar morphology but exhibit significant differences in device performance, which can be understood from the results measured with Kelvin probe force microscopy. The 2D surface potential mapping at the organic/organic interface with submonolayer morphology provides a striking contrast between the two heterostrutures, which is directly related to the interface electronic properties. Moreover, a charge transfer effect was clearly observed in the pentacene/p-6P system which further enhanced the charge transport in the devices. This study provides a simple route to gain thorough understanding of organic/organic interfaces.