We considered that properties of the microenvironment surrounding cells are important for the control of the cell functions. Cytocompatible polymer hydrogels are good candidates to study such microenvironment. Here, we prepared spontaneously forming hydrogels composed of two polymer systems, namely poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate-co-p-vinylphenylboronic acid) (PMBV) and poly(vinyl alcohol) (PVA). The PMBV/PVA hydrogels could be reversibly dissociated by the addition of d-sorbitol. The storage modulus was measured for evaluating the mechanical properties of the PMBV/PVA hydrogels. The storage modulus could be controlled in the range 0.30-2.5 kPa by changing the cross-linking density of the hydrogels. After pluripotent stem cells were encapsulated within the PMBV/PVA hydrogels during the preparation of the hydrogel under normal cell-culturing conditions, the proliferation rate and the cell cycle of the encapsulated cells were observed. Cells lived for more than three days in every PMBV/PVA hydrogel. However, the proliferation significantly depended on the storage modulus of the hydrogels. Although the cell cycle of the initial cells was heterogenous, it developed uniformity toward the G1 phase when the cells were encapsulated within the PMBV/PVA hydrogel with a storage modulus of 1.1 kPa for three days. That is, the mechanical properties of the PMBV/PVA environment influenced the biological functions of the cells encapsulated in the hydrogels. From these results, we conclude that PMBV/PVA hydrogels are useful for adjusting cell cycles and proliferation, thus providing uniform cells for applications in the field of cell engineering.