Combustion intermediates of a cyclic oxygenated hydrocarbon, 1,4-dioxane, were studied with the tunable synchrotron vacuum ultraviolet photoionization and molecular-beam mass spectrometry (MBMS) technique. A fuel-rich premixed laminar 1,4-dioxane/O-2/Ar flame at low pressure with an equivalence ratio of 1.80 was investigated in the present work. A total of 20 intermediates were observed, and their mole fraction profiles are calculated. Aromatic intermediates were not observed, and this was a prominent difference between the fuel-rich flames of 1,4-dioxane and previously studied noncyclic oxygenated hydrocarbons. The fuel-rich 1,4-dioxane flame could be divided into four zones, and formation routes of the intermediates were proposed. The discussion on the pollutant emissions showed that some light toxic molecules were produced from 1,4-dioxane combustion; however, toxic aromatics and soot emissions were possibly avoided.