The high-resolution infrared spectrum of the fundamental band ν12 (ring breathing) of the chiral molecule propylene oxide (CH3CHCH2O) was recorded at room temperature and under jet-cooled conditions using a quantum cascade laser at 8 μm. The observed lines with quantum numbers J ≤ 55 and Ka ≤ 21 were assigned to strong b- and c-type bands, and some low J transitions were classified as weak a-type transitions. The lines were fitted using a Watsons A-reduced Hamiltonian in the Ir representation. From the rovibrational analysis the band origin as well as the rotational constants and four quartic centrifugal distortion constants were derived.