Detection of gas pressure can be done using singlemode-multimode-singlemode (SMS) fiber structure as the sensor. The mechanism of detection utilizes gas pressure in the tube to inflate the membrane. Changing shapes of the membrane will cause curvature in the SMS fiber structure which attached to the membrane. As the curvature changes, results on changing spectrum of interferences, including changing peak wavelength or transmission power. Detection of gas pressure can be done also for the inflating and deflating the gas tube process. The experimental results shown that changes due to changing gas pressure on transmission power was consistent, while changes in peak wavelength was not consistent. The detected gas pressure range is 0 Psi-6 Psi with a linear range of 0-6 Psi and resolution of sensor is 0.18 Psi. Sensitivity of the sensors produced in the inflating and deflating process are 0.078 dBm/Psi and 0.077 dBm/Psi, respectively.