Abstract <p>The mechanical and thermal properties of polypropylene (PP) nanocomposites reinforced with C_60/70 fullerenes, multi-walled carbon nanotubes (MWCNTs) and NiO nanoparticles were systematically examined. Nanocomposites containing controlled nanofiller loadings were fabricated and characterized by tensile testing and thermogravimetric analysis. Incorporation of C_60/70 fullerenes yielded the most pronounced mechanical enhancement, increasing tensile strength from 31.41 to 31.87 MPa and elongation at break from 34 to 40%. MWCNTs produced moderate improvements (up to 29.77 MPa and 38%), contributing primarily to matrix stability. Thermal analysis showed that all nanofillers improved the thermo-oxidative resistance of PP. Fullerenes increased decomposition temperatures (<i>T</i>₁₀ = 250°C, <i>T</i>₂₀ = 300°C, <i>T</i>₅₀ = 360°C), elevated τ_1/2 from 63.2 to 68.8 min, and raised activation energy from 145.45 to 189.48 kJ/mol. MWCNTs similarly enhanced thermal thresholds (<i>T</i>₁₀: 135 → 250°C; <i>T</i>₂₀: 265 → 300°C; <i>T</i>₅₀: 335 → 350°C) and extended τ_1/2. Overall, C_60/70 fullerenes provide dominant mechanical reinforcement, while thermal stability arises from their radical-scavenging ability combined with the structural and buffering contributions of MWCNTs and NiO. These findings offer design principles for high-performance PP-based nanocomposites.</p>