The concept of memcapacitance, defined as a memorized capacitance change, has been suggested and demonstrated with several structures. In particular, the memcapacitance in MOS capacitor structure is advantageous in that its capacitance change can modulate the drain current in MOS-based transistor. The nonvolatile capacitance change in MOS structure can be applied to nonvolatile memory by altering the drain current as well as the threshold voltage. In addition, it can be adopted in artificial synaptic device mimicking human brain motions, where the drain current corresponding to the synaptic weight can be altered by capacitance change in MOS as adaptive motion of synapse. In this study, the memcapacitance characteristics of Al/SiO2/TaOx/n-IGZO MOS structure were investigated for the application to synaptic transistor. The MOS structure exhibited analog, polarity-dependent, and reversible memcapacitance through the redistribution of oxygen ions between TaOx and n-IGZO. When a positive bias was applied to the Al top electrode, an accumulation capacitance increased gradually, implying increased permittivity of TaOx as a possible result of the migration of oxygen ions from n-IGZO to TaOx. Consequently, the depletion capacitance increased owing to the increased oxygen vacancy concentration in the n-IGZO layer. The capacitances could be restored by applying a negative potential to repel oxygen ions from TaOx back to n-IGZO. Using this phenomenon, this MOS structure could be applied to nonvolatile memory and synaptic transistor with analog increase and decrease of capacitance leading to the change of memory state and the synaptic potential and depression behavior, respectively. The detailed memcapacitance characteristics of Al/SiO2/TaOx/n-IGZO with respect to the thickness of each layer and voltage application condition, and so on.