Abstract: This paper investigates the core and cladding effective area and splicing loss behavior of a square lattice photonic crystal fiber. These behaviors of square lattice photonic crystal fiber are also compared with the hexagonal photonic crystal fiber. Effective index method is applied for the numerical calculation and the plot has been analyzed by using MATLAB. It has been observed that by choosing some sufficient dimensional parameter a square lattice photonic crystal fiber has sufficiently large effective area and nearly zero splice loss of 0.0006dB at 1.55µm.