In this paper, two highlysensitive photonic crystal fiber (PCF) structures with microstructure core and claddinghave been demonstrated for Ethanol sensing. Themicrostructure core of both proposedPCFs is designed with supplementary holes in an octagonal formation. We have investigated therelative sensitivity and the confinement loss of the proposed PCF structuresemploying a fullvectorial finite element method (FEM). The proposed PCFs work at a widetransmission band covering 0.8 µm to 2 µm and exhibit high sensitivity and lowconfinement loss simultaneously. The numerical analysis shows that the circular shape of air holes in the first ring is a moresalient attribute forincreasing sensitivity and the presence of the square shape of air holes in the first ring showsbetter performance to reduce confinement loss.