The progress in the technology of manufacturing new materials increases the usage of Terahertz (THz) region, which is considered as the last explored region of electromagnetic spectrum. In biological, chemical, sensing and detecting applications THz region is started to be used widely. We proposed a unique fishnet metamaterial (MTM) absorber and metasensor that can be used to detect and characterize new materials which are produced for THz region. First of all, the reflection and absorption characteristics of fishnet MTM were analyzed. Perfect absorption was achieved by 97.3% absorption rate and with assisting from electric field and surface current distributions we explained the electromagnetic theory behind the frequency resonances. For sensory application, the material that is going to be detected was added as a single and double overlayer (OL) to proposed fishnet MTM and fishnet MTM absorber sensor. The shifts in the resonant frequencies were observed for the change in permittivity and thicknesses of the OL materials. From the analysis of resonant shifts it is proved that the proposed structure shows high sensing ability in THz region.