In this study, two different carbon fillers (Thermocarb TC-300 synthetic graphite and Fortafil 243 carbon fiber) were added to Vectra A950RX liquid crystal polymer to produce single filler composites with filler concentrations of up to 80 wt % (71.4 vol %) and multiple filler composites that contained varying concentrations of both synthetic graphite and carbon fiber. The through-plane and in-plane thermal conductivity for each formulation was measured. For the single filler synthetic graphite and carbon fiber composites, the Nielsen model was applied to the experimental through-plane thermal conductivity data. The parameters obtained from the single filler models were then used along with a variation of the original Nielsen model to predict the through-plane thermal conductivities of the multiple filler composites. In-plane thermal conductivity models were also developed using a correlation involving the square root of the product of the composite in-plane and through-plane thermal conductivities. This model was applied to the single filler synthetic graphite and carbon fiber composites. A variation of this model was then used to predict the in-plane thermal conductivity for composites containing both fillers. All the models presented in this work showed good agreement with experimental data. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2914-2923, 2008