In the field of analytical chemistry and its instrumentation, microsystem technology has been most remarkable, because it leads to on-site and real-time monitoring, high-speed and high-throughput analysis, resulting from a small sample volume, rapid operation procedure and a small measuring device space. Although atmospheric environment has a lot of pollutants, a few researchers deal with gas phase since most of these researchers have been proposed for analyzing liquid samples. Because of large differences between physical parameters of gas and liquid phases, such as viscosity and compressibility, the control of a stable gas–liquid equilibrium system in a microchannel was relatively difficult. If the chemicals in the environment can be easily taken into microsystems, their application to sample pretreatment microchips and downsized mass spectrometer system will spread further. After analyzing simple gas–liquid equilibrium system on microchip, for example, a gas–liquid contacting pretreatment microsystems via porous material was described, and several novel gas, liquid, and solid sample pretreatment methods were developed by utilizing mass transfer microsystems from gas, liquid, and solid phases to liquid phase, respectively. In the environmental monitoring of gas, liquid, and solid samples, on-site and continuous monitoring microsystems are required for hazardous nitrogen dioxide, sulfur dioxide, ozone, formaldehyde, and volatile organic compounds in the parts per trillion by volume (pptv) level in atmospheric environment. Trace and precise analysis microsystems are needed for hazardous metal ions, harvesters, endocrine desrapter compounds, nutrition phosphoric and nitrogen compounds at the parts per million (ppm) level in wastewater and water samples. Environmental solid sample pretreatment microsystems are really necessary for various kinds of solid samples such as nano meter-size particles, diesel exhaust particulates, flied ash, suspended solid materials, carbon, and soil samples because such samples contain hazardous and carcinogenic compounds like dioxine, polychlorimated biphenyls, and endocrine disruptor compounds at the lower levels than the ppm level. A micro mass spectrometer was developed for a powerful tool by combination with micro chemical pretreatment systems to solve industrial pollution and environmental monitoring problems.