External radiation exposure to uranium is generally not a major concern due to the long half lives of the isotopes of natural uranium.Uranium is a health hazard only when it is taken into the body.Bioavailability of the inhaled or ingested uranium is determined by its speciation in biological fluids, such as lung fluid and blood.The challenge of uranium speciation analysis is the dissociation of the inorganic uranium species, mainly, uranyl carbonates, i.e.separation of the uranium species always accompanied by the dissociation of the species.Only single peak was observed in previous work of uranium speciation analysis using instrumental separation techniques.In this work, capillary electrophoresis with on capillary complexation technique was used to allow the uranium species to be complexed to complexing agent in a buffer solution when migrating and to be separated within the time scale of the dissociation of the species.Several complexing agents were found to work efficiently.Computer modeling of the uranium speciation distribution in biological fluid was also performed to compare with the experimental results.