PROBLEM TO BE SOLVED: To provide a microchip made of a resin with a microchannel with a channel sealed by an upper substrate which is transparent and absorbs little in ultraviolet region, is minute and has satisfactory surface smoothness, and is high in dimension accuracy. ;SOLUTION: The microchip for optically measuring a liquid sample has at least both a lower substrate with the microchannel through which the liquid sample flows and the upper substrate made of a flat film. At least the lower substrate is made of a transparent hydrocarbon-based polymer expressed by Fig. (1). At least the surface of the lower substrate on the side with the channel is treated with oxygen plasma, and then the lower substrate and the upper substrate are subjected to thermocompression bonding at temperatures lower than the glass-transition temperature (Tg) of the transparent hydrocarbon-based polymer to obtain the microchip. ;COPYRIGHT: (C)2003,JPO