Abstract Novel PSMA-POSS nanocomposites were prepared, in which N-phenylaminomethyl polyhedral oligomeric silsesquioxane (POSS) was conducted as crosslink agent to incorporate to poly(styrene-co-maleic anhydride) (PSMA). POSS was introduced by one-step reactive solution blend in amounts of 1–30 wt%. FTIR measurement evidenced the occurrence of amidation reaction between the anhydride group of PSMA and the secondary amino group of POSS. This reaction turned out to promote POSS well dispersed in the polymer matrix, and the PSMA-POSS hybrids showed no macro phase separation even if POSS concentration was up to 30 wt%. DSC results showed that the glass transition temperature ( T g ) increased to 168 °C with the increase of POSS loading. Dynamic mechanical thermal analysis (DMTA) revealed the storage modulus at high temperature increased with the addition of POSS due to the formation of a permanent network. Incorporation of POSS also improved the thermal properties of PSMA-POSS composites.