We proposed and developed an integrated fluorescent oxygen gas-sensor probe module based on asymmetric 1  ×  2 optical waveguides that can transmit power from an optical source and the fluorescence signal with high efficiency simultaneously. The fluorescent oxygen gas-sensor comprises an optical source part, optical detector part, and optical sensing probe part. The optical sensing probe comprises asymmetric 1  ×  2 optical waveguides coated with an oxygen-sensitive fluorescent film on the end face of the optical waveguide. This optical probe module can transmit the optical power and fluorescence signal with high efficiency because of the same optical path for transmission of the optical source and the fluorescence signal. In addition, this structure facilitates an integrated miniature oxygen-sensor module. We optimally designed the asymmetric 1  ×  2 optical waveguides with an asymmetric structure and different two core size. Then, we fabricated the polymeric asymmetric optical waveguides using the UV imprint lithography process suitable for cost-effective mass production. The optical oxygen-sensor probe transmitted the optical source power and the fluorescence signal with 80% and 82% efficiency, respectively. An oxygen-sensitive fluorescent film was coated on the end face of the optical waveguide by using the spray coating method. The oxygen-gas detection sensor constructed using this optical probe module with 1  ×  2 asymmetric optical waveguides could measure the concentration with 0.3% resolution for a gas concentration range of 0% to 25%. This optical oxygen-sensor probe module facilitates a compact, simple, and cheap measurement system.