An integrated polydimethysiloxane (PDMS) microfluidic system which is composed of two pneumatic micropumps and one micromixer is developed for high-accuracy detection of insulin. The detection method is based on coupling the highly specific technique of 'double-antibody sandwich immunoassay' with the sensitive chemiluminescence of Luminol-Hydrogen Peroxide (H2O 2). The immune reactions and other related processes are carried out in the microfluidic system semi automatically. Sample transportation in the microfluidic system is accomplished by two pneumatic PDMS micropumps. Chemiluminescent measurement is conducted in a separate PDMS micromixer using a double-channel syringe pump to inject reagents. Light emitting from this mixer is detected by a highly sensitive photometer when the chemiluminescent regents flow through the mixer chamber. The results indicate that at an actuation pressure of 10psi, a mixer actuation frequency of 5Hz, and an injecting flow rate of 0.5 ml/min, the detection limit of the microfluidic system for insulin is about 10^-10 M.