Microfluidic-based heterogeneous immunoassays are reviewed in this article by first introducing the principle of immunoassay, followed by a discussion of microfluidic-based technology. Microfabrication, surface modification, solution dispensing and detection technology are discussed and their applications to biomolecular detection reviewed. In the future, improved manufacturing processes and integrated assay systems in an automatic fashion with a reduced assay time and reagent consumption will allow for the effective detection of biomolecules that are of interest in medical diagnostics, drug discovery and bioterrorism.