Microwave absorber able to inhibit the reflection of electromagnetic radiation. Microwave absorbers are used in an anechoic chamber along with its wall, ceiling and floor for the electromagnetic compatibility (EMC) and electromagnetic interference (EMI) evaluation. This research is to develop a flat shape of biomass absorbers using an agricultural material. The main material used in constructing the flat absorber is a natural bamboo. The flat shaped absorber is chosen because it could reach the standard set in the specified industry and suitable to be used in the microwave frequency range. Cylindrical bamboo with different radius have been used for this study. Radius 0.2 cm for Design 1 and 1 cm for Design 2. The range of frequencies are set in the range from 1 GHz to 12 GHz. The result of microwave absorber is analyzed for its absorption performance. The generated result from the technique shows that the flat stick bamboo microwave absorber operates the best in Design 2 with 34.9% of absorption performance compared with Design 1. The overall results in different angles for both designs are analyze and compared.