While cells attach, spread, migrate, proliferate, and differentiate in 3D micromechanical environments, the mechanical factors of these environments influence the shapes, sizes, and adhesion forces of the cells. The effects of substrate stiffness on cell behaviors have been extensively studied; however, the effects of substrate curvature are not well documented. The curvature of the surface to which cells adhere can have profound effects on cell behaviors. To reveal these cell mechanobiological responses to substrate curvatures, here we introduce a novel, unique, simple, and flexible class of substrates, polyacrylamide gels embedded with micro glass balls ranging in diameter from 5 μm to 4 mm, to culture cells. NIH-3T3 fibroblasts and human mesenchymal stem cells (hMSCs) are cultured on these glass ball embedded gels. Morphologies of cells growing on glass balls are analyzed by using an optical microscope and a 3D confocal laser scanning microscope. The cell behaviors on micro cylindrical glass tubes having similar diameters to the glass balls are also compared. We find that, among the used diameters of glass balls, the minimum diameter of a glass ball on which an hMSC can attach and spread is 500 μm whereas this number for an NIH-3T3 fibroblast is 58 μm. In contrast to the well-spread morphologies with randomly-multiple lamellipodia for the hMSCs growing on the flat glass plates, the morphologies of the hMSCs growing on the glass balls are almost uniformly spindle-shaped with two lamellipodia. The sensitivities of the attachment and spreading morphology of an hMSC to substrate curvature are very different from those of a fibroblast. The RT-PCR analysis reveals that the substrate curvature alone can induce adipogenesis of the hMSCs. These findings imply that substrate curvature has profound effects on stem cell behaviors, and detailed and in-depth studies on these effects and their underlying biophysical mechanisms are necessary. To the best of our knowledge, this is the first experimental attempt to study cell responses to spherically shaped substrates. Our cell culture experiments to date imply that this class of substrates, micro glass ball embedded gels, can be powerful tools to study cell mechanobiological responses to substrate curvatures, related cell and tissue engineering researches, and biomedical applications.