A mathematical model was developed to investigate the effect of transient thermal effect on capillary electroosmotic flow. The model consisted of the Poisson-Boltzmann equation

the Navier-Stokes equation

and the energy equation coupled through temperature. Transient developments of the velocity and temperature profiles were obtained. Since the change in the velocity profile with time was mainly caused by the temperature change

the evolutions of the velocity profiles and temperature profiles always synchronized with each other.The developments of temperature profile

as well as velocity profile due to thermal effects were obtained and discussed under different cooling conditions and different electric field strengths. The present model enabled the determination of a suitable cooling condition at the outer surface of the capillary tube to avoid overheating and provided an adequate migration velocity for given dimensionless numbers

which characterized thermal hydraulic fluid flow due to electrokinetic effects.