The interface between carbon fibers (CFs) and matrix resin makes a critical contribution to bulk performance of composites. In order to enhance interfacial properties and anti-hydrothermal aging behaviors of methyl phenyl silicone resin (MPSR) composites, octamaleamic acid-polyhedral oligomeric silsesquioxanes (POSS-acid) were directly grafted onto CFs surface by chemical bonding for the first time. Surface chemical groups and morphologies of CFs before and after POSS-acid grafting were systematically characterized. Scanning electron microscopy and atomic force microscopy images showed a uniform distribution of POSS-acid on the fiber surface and the improved surface roughness. POSS-acid cages grafting could improve obviously the fiber polarity, wettability, and free energy by dynamic contact angle analysis testing. The interlaminar shear strength (ILSS) of MPSR composites reinforced with the POSS-acid-modified CFs (CF-POSS) was 45.01 +/- 1.69 MPa, which increased by 52.73 % compared to that of MPSR composites reinforced with untreated CFs (29.47 +/- 0.94 MPa). And, impact strength of CF-POSS composites (77.69 +/- 2.83 kJ m(-2)) was increased by 32.89 % compared to that of untreated CF composites (58.46 +/- 1.91 kJ m(-2)). Moreover, ILSS of CF-POSS composites after hydrothermal aging treatment was 40.89 +/- 1.51 MPa with a decrease of just 9.15 % compared to that of untreated CF composites (20.52 +/- 0.65 MPa) with an obvious decrease of 30.37 %. Meanwhile, POSS-acid functionalization did not decrease fiber tensile strength. Based on our design starting from simple chemistry and inexpensive materials, such hierarchical reinforcements with improved interfacial strength and anti-hydrothermal aging behaviors have great potential in advance polymer matrix composites.