A theoretical analysis, based on the lubrication theory, of the Joule heating effect on a purely electroosmotic flow (EOF) of non-Newtonian fluids through a slit microchannel is presented. The Joule heating effects are caused by an imposed electric field, where the zero-shear-rate viscosity and electrical conductivity of the liquid are assumed temperature-dependent. Due to Joule heating effects, temperature gradients in the liquid make the fluid properties change within the microchannel, altering the electric potential and flow fields. A consequence of the above is the appearance of an induced pressure gradient along the micro-channel, which in turn modifies the normal plug-like electroosmotic velocity profiles. This modification of the electroosmotic fluid flow could cause significantly higher dispersion than that from parabolic-like electrophoretic flow profile, limiting its use. In addition, it is pointed out that, depending on the fluid rheology and the used values of the dimensionless parameters, the velocity, temperature and pressure profiles in the fluid are substantially modified. The dimensionless temperature profiles in the fluid and the microchannel wall are obtained as function of the dimensionless parameters involved in the analysis, and the interactions between the coupled momentum, thermal energy, and potential electric equations are examined in detail. (C) 2012 Elsevier B.V. All rights reserved.