polydimethylsiloxane (PDMS) based microsystems have successfully been fabricated and characterized for studying protein crystals utilizing both UV-visible spectroscopy and X-ray crystallography. Transmittance tests have been conducted with PDMS and glass substrates; the measurements indicate that in PDMS, unlike glass, the emerging intensity is higher than 50% of the incident intensity as long as the total optical path is shorter than 100μm. Indeed, both the UV-visible spectrum and X-ray diffraction of a protein crystal enclosed in a PDMS device are almost identical to those of the crystal alone. Hence, PDMS is suitable as substrate material in device fabrication to study protein crystals. In glass, however, the UV-visible spectrum is significantly distorted and the X-ray diffraction pattern is rather weak resulting in poor signal to noise ratio. Furthermore, microsystems integrated with microchannels allowing continuous exchange of buffer solution around the protein crystals have been tested; this would greatly enhance the potential to induce, trap and characterize functional states in proteins.