Currently gold nanoparticles are widely used in optical bioassays because of their characteristics, such as good biocompatibility, excellent optical performance, special catalytic activity and the convenience of controlled fabrication. This review describes the application development of gold nanoparticles in various optical biosensors, including colorimetry, scanometry, dry-reagent strip, surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS), chemiluminescence and fluorescent biosensors. Firstly, we present the underlying principles that contribute to the enhanced detection capability of gold nanoparticles, taking advantage of their unique characteristics in these bioassay methods. We then demonstrate selected examples to illustrate the development of each method, focusing on the performance improvement of the biosensor, such as sensitivity, selectivity and so on. Finally, we conclude and discuss the future prospects of using gold nanoparticles in biosensors.