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In this paper, the sensitivity characteristics of Fabry-Perot (F-P) hydrostatic pressure sensor based on two different hollow-core (HC) microstructured optical fibers are experimentally and theoretically investigated. The sensors are fabricated by simply splicing a length of HC fiber to singlemode fibers. Hydrostatic pressure is measured by monitoring the wavelength shifts of the interferometric fringes as a result of the two reflection beams at the splicing points. The measured pressure sensitivities of F-P sensors fabricated on the simplified HC microstructured fiber and hollow-core photonic bandgap fiber (HC-PBGF) are - 17.3 and - 23.4 pm/MPa, respectively. Theoretical investigation is then carried out based on the analysis of elastic properties for the individual fibers. The calculated result suggests that the pressure sensitivities are dominantly determined by the induced changes in cavity length. In comparison, the contribution of mode-index change is slight. The mechanisms behind the mode-index changes for the two fibers are clarified by analyzing the deformation of the fiber structure under pressure. The holey microstructure is highly deformable compared to the solid fiber, which provide another dimension for the implementation of tunable photonic devices.