In this work, lanthanum strontium manganite (LSM)‐reinforced polybenzoxazine (PBZ) and PBZ/epoxy hybrid composites have been developed with enhanced thermal, mechanical, dielectric, and flame‐retardant performance. LSM particles was synthesized via a microwave combustion method followed by surface‐functionalization using 3‐glycidyloxypropyltrimethoxysilane (GPTMS). The functionalized LSM was incorporated into bisphenol‐F and aniline based benzoxazine (BF‐a) and BF‐a/Bisphenol‐F epoxy (DGEBF) (50/50) blends followed by thermal curing to obtain composites. An incorporation of LSM improved thermal stability, with the initial degradation temperature (T 5 %) of poly(BF‐a) increased to 383°C from 346°C and the value of char yield to 59.1% from 42.8%. The heat resistance index (HRI) increased from 205°C to 224°C, while the limiting oxygen index (LOI) increased from 34.6 to 41.1. The value of tensile strength increased up to 116 ± 3 MPa for PBZ/DGEBF composites. Shore D hardness increased from 81 ± 2 to 95 ± 1.5, while the coefficient of thermal expansion decreased from 52.5 × 10 −6 °C −1 to 37.7 × 10 −6 °C −1 , indicating enhanced dimensional stability. Dielectric analysis indicated an increase in dielectric constant from 3.50 to 5.61 for poly(BF‐a) composites and from 3.90 to 7.35 for PBZ/DGEBF composites at 10 wt% LSM loading, while maintaining low dielectric loss (0.002–0.019).