The effect of arrays' size on magnetization reversal in nanodisks has been investigated. Symmetrical arrays of Py nanodisks with diameter 600 nm and thicknesses 10, 22, and 30 nm has been studied by magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM). It has been found that the increase in a number of nanodisks leads to the fall of magnetic vortex annihilation field. The dependence of the vortex nucleation field has oscillating behavior due to magnetostatic interaction between adjacent nanodisks. The dependences of critical fields of vortex nucleation and annihilation calculated within “rigid” vortex model are in a good agreement with experimental results. Using MFM it has been demonstrated that transition from single domain state to C-state occurs in nanodisks at different applied magnetic fields. We have revealed that the coincidence of magnetization switching in nanodisks rises with increasing of magnetostatic interaction.