This thesis addresses some important issues when designing microfluidic systems for hot pressurized water. The properties and behavior of water at elevated temperatures and in micro scale is briefly reviewed, and opportunities and possible problems of using hot pressurized water in microfluidic devices are brought up. Experimental work was focused on corrosion resistance for commonly used microsystem materials in hot pressurized water, and the microfluidic behavior for hot pressurized water. An experiment system was successfully designed, assembled and used for corrosion resistance experiments in hot pressurized water. Corrosion resistance tests were performed for some common materials used in microfluidic and microsystems (silicon, stainless steel grade 304, silicon carbide, aluminum nitride, aluminum oxide, soda-lime glass and borosilicate glass) in deionized water and in low concentration HCl (0.1 mM) at two different temperatures (180oC and 270oC). All of the tested materials, except soda-lime glass, showed a good overall performance in the low temperature range. In the high temperature range, all materials showed signs of corrosion to some extent. Severe damages and high corrosion rates were observed for silicon and the two glasses, and stainless steel 304 showed signs of pitting corrosion. A microfluidic study identified some major issues needed to be overcome to make future microfluidic studies with hot pressurized water possible. Important observations included the importance of a short traveling distance for a hot micro flow to avoid rapid cooling, and to choose a suitable dye to avoid particles clogging thin capillaries and micro channels.