The kinetics of propanal oxidation was studied in a jet-stirred reactor (JSR) at atmospheric pressure. The investigated temperature range is from 450 to 800 K at two different equivalence ratios (0.35 and 4.0). Thanks to the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), critical intermediates were identified, including methylperoxy, methyl hydroperoxide, ethylperoxy, ethyl hydroperoxide, α-lactone, β-propiolactone and ketohydroperoxides. A kinetic model for propanal oxidation was also developed and validated against the present experimental results, as well as those available from the literature. Main chain-branching pathways under the investigated conditions were analyzed based on present experimental data and kinetic model. The O2 addition reaction to the propanoyl radical and subsequent oxidation reactions play an important role in determining the oxidation rate of propanal under fuel-lean conditions, especially in the low-temperature oxidation region. Under fuel-rich conditions, the decomposition of the propanoyl radical is predominant and C2H5 relevant reactions consequently determine the kinetics of oxidation of propanal.