The bio-microfluidic systems are usually encountered with non-Newtonian behaviors of working fluids. The theological behavior of some bio-fluids can be described by differential viscoelastic constitutive equations that are related to PTT and FENE-P models. In the present work, thermal transport characteristics of the steady fully developed electroosmotic flow of these fluids in a slit microchannel with constant wall heat fluxes have been investigated. The Debye-Huckel linearization is adopted and the effects of viscous dissipation and Joule heating are taken into account. Analytical solutions are obtained for the transverse distributions of velocity and temperature and finally for Nusselt number. Two different behaviors are observed for the Nusselt number variations due to increasing epsilon(ge)We(2) which are an increasing trend for positive wall heat flux and a decreasing one for negative wall heat flux. However, the influence of epsilon(ge)We(2) on Nusselt number vanishes at higher values of the dimensionless Debye-Huckel parameter. It is also realized that the effect of viscous heating is more important at small values of both epsilon(ge)We(2) and the dimensionless Debye-Huckel parameter. Furthermore, the results show a singularity in Nusselt number at higher negative values of the dimensionless Joule heating parameter. (C) 2011 Elsevier Ltd. All rights reserved.