Organic montmorillonite (MMT) modified by 1,3-dihexadecyl-3H-benzimidazolium bromide (Bz) was used to prepare polyphenylene sulfide (PPS)/MMT composites by melting intercalation. The PPS/MMT composites showed mixed morphology, being comprised of exfoliated and intercalated structures with slight agglomerates. The tensile property of PPS/MMT composites was significantly improved due to the good dispersion of the MMT nanolayers. The test results showed that the tensile strength retention of PPS/MMT composites was higher than that of pure PPS after the oxidation treatment. Moreover, FTIR and XPS analyses were also used to evaluate the oxidation resistance of PPS composites. The FTIR analysis confirmed that adding MMT could better limit the damage of the C–S group and retard the generation of sulfuryl groups (–SO2–) during the oxidation treatment compared to pure PPS. The XPS analysis also suggested that the addition of MMT could reduce the chemical combination of the elements sulfur (S) and oxygen (O) during oxidation treatment. Furthermore, the MMT nanolayers could also promote the transfer of S from a C–S bond into an –SO2– group.