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The aim of this study was to investigate the pozzolanic effect (PE) and filler effect (FE) of rice husk ash (RHA) on the mechanical properties and microstructure of brick aggregate concrete (BAC). For this, concrete cylinders (100 mm × 200 mm) were prepared with 0–25% RHA with water-to-binder ratios of 0.50 at a constant mix-ratio of 1:1.5:3 and cured in water. Test results revealed that the mean particle size of RHA decreases with increasing grinding time. The compressive strength ( ) of BAC due to filler effect are 58.56–94.62% less compared to the pozzolanic effect of RHA for the 10%–25% replacement of cement. Meanwhile, the 15% RHA showed the maximum of BAC due to pozzolanic effect of RHA. The tensile strength ( ) and flexural strength ( ) of BAC due to pozzolanic effect are 60%–150% and 25%–150% higher than that of filler effect of RHA for the 10%–25% replacement of cement respectively. The modulus of elasticity ( ) and Poisson's ratio ) of BAC due to pozzolanic effect are 2%–29% and 27%–43% greater than that of filler effect of RHA for the 10%–25% replacement of cement respectively. BAC with 10–20% RHA shows a dense and homogeneous microstructure. Therefore, inclusion of RHA as a partial replacement of cement possesses a significant pozzolanic effect than the filler effect on the mechanical properties and microstructure of BAC.