Scaffold design has a critical role in tissue engineering as scaffold features affect cell attachment and proliferation. Size scale similarities of electrospun nano-/microfibrous scaffolds with a native extracellular matrix have been appealing for tissue engineering applications and numerous studies have investigated the effect of different aspects of nano-/microfibrous scaffolds such as fiber diameter, thickness of nano-/microfibrous scaffolds on cell behavior. In this study, electrospun poly (epsilon-caprolactone) (PCL) microfibrous scaffolds were fabricated with nanosized pores on the surfaces of fibers created by the electrospinning of PCL solution with a highly volatile solvent in a humid ambient and the effects of nanopores on the attachment and proliferation of epithelial kidney cells (Vero) and mesenchymal stem cells (MSCs) were investigated. Morphology and hydrophilicity of the scaffolds were analyzed by scanning electron microscopy (SEM) and the video contact angle system and evaluation of cells proliferation and morphology of them on scaffolds were performed by MTS assay and SEM. Our results showed that relative humidity (RH) and electrospinning parameters affect the creation of pores on the surface of scaffolds. Furthermore, MTS assay and SEM results showed that nanopores on the surface of microfibers enhance initial attachment and proliferations of Vero and MSCs cells, which may be related to an increase in surface area of the porous fibrous scaffold compared to the nonporous fibrous scaffold.