AbstractDental follicle cells (DFCs) are osteogenic progenitor cells and are well suited for molecular studies of differentiation of alveolar osteoblasts. A recent study examined the metabolism in DFCs during osteogenic differentiation and showed that energy metabolism is increased after 14 days of differentiation (mid phase). However, previous studies have examined proteomes at early (2 h, 24 h) or very late (28 days) stages of differentiation, but not during the phase of increased metabolic activity. In this study, we examined the phosphoproteome at the mid phase (14 days) of osteogenic differentiation. Analysis of DFC phosphoproteomes showed that during this phase of osteogenic differentiation, proteins that are part of signal transduction are significantly regulated. Proteins involved in the regulation of the cytoskeleton and apoptosis were also increased in expression. As osteogenic differentiation induced oxidative stress and apoptosis in DFCs, the oxidative stress defense protein, catalase, was also upregulated during osteogenic differentiation, which supports the biomineralization of DFCs. In summary, this study revealed that during the middle phase (14 days) of osteogenic differentiation, processes in DFCs related to the control of cell organization, apoptosis, and oxidative stress are regulated.