We analyze the symmetric ion-size effect (i.e. cation and anion have same size) on the osmotic pressure in cylindrical nanochannels. In nanochannels the Electric Double Layer (EDL) thickness becomes comparable to the width of the nanochannel resulting in overlapping phenomena. The modified Poisson-Boltzmann (mPB) equation is the governing equation to estimate the osmotic pressure from the electric potential distribution obtained through numerical simulation with constant surface potential condition. The numerical simulation is based on the finite element method. The variation of osmotic pressure with increase in steric factor is investigated. An effort is also made to compare the results of cylindrical and rectangular nanochannels