This research aims to study thermal and mechanical properties of highly filled alumina composites utilizing polybenzoxazine as a matrix. The condition for the compression molding to produce highly filled alumina-polybenzoxazine composites was at the temperature of 200oC, and the pressure of 15 MPa in a hydraulic hot-press machine for 2 hours to assure a fully cured specimen. The composition of alumina filler was achieved to be in the range of 50 to 83% by weight. The densities of the obtained composites were found to be in a range of 1.19-2.811g/cm3 as predicted by rule of mixture. The experimental results revealed that at the maximum alumina content of 83wt% or 60vol% filled in the polybenzoxazine, storage modulus at room temperature of the specimen was raised from 5.9 GPa of the neat polybenzoxazine up to about 45.3GPa in the composites which is about 600% improvement.The glass-transition temperatures (Tg) of the prepared composites were observed to be ranging from 178 to 188oC and the values substantially increased with increasing the alumina contents. The degradation temperature (Td) of the prepared composites were observed to be ranging from 336 to 389oC. Furthermore, at alumina content of 83wt% in the polybenzoxazine, the composite’s flexural modulus and flexural strength were found to be as high as 36.4GPa and 142.42MPa, respectively, whereas the Vickers hardness was determined to be as high as 1124 MPa. Water absorption of this filled system was relatively low with the value of about 0.054% at 24 hours. Consequently, the data on thermal propertiesand mechanical properties of the alumina filled polybenzoxazine composites are highly attractive for wear resistance and electronic applications.