This paper presents a material characterization method by using microwave signals at the frequency of 2.4 GHz and 5.2 GHz. Two types of circular loop FSS are used to filter the transmission waves at both selected frequency bands. The chosen materials for characterization are distilled water, bicarbonate water, rock and black soil. The measurement is conducted in an indoor environment with the distance of 30 mm. The materials are characterized based on reflection and transmission signals extracted from measured S-parameters. The results showed that black soil has the highest reflection loss at the frequency of 2.4 GHz while distilled water has the highest reflection at the frequency of 5.2 GHz. Meanwhile, rock showed minimum transmission losses of -18 dB and -26 dB at 2.4 GHz and 5.2 GHz respectively. This characterization method can be used to identify different materials such as liquid or solid structure.