Composites of silicone matrix filled with phosphor are widely used in light emitting diodes (LEDs) packaging. Its thermal conductivity is one of the important properties for LED thermal analysis. In this paper, a unit cell model (UCM) that includes interface resistance between phosphor and silicone matrix was built and applied to predict the thermal conductivity of uncured silicone/phosphor composites at different phosphor volume fractions. The thermal conductivities of seven uncured silicone/phosphor composites samples were measured for comparison with modeling results. The comparison shows that the model result matches to the experimental data within +/- 6% at the low volume fraction from 3.8% to 25%. Both the experiment and modeling results show that thermal conductivity of the composite has a sudden increase when volume fraction increases to near 40%, which can be explained by the percolation theory. For higher volume fraction, the effect of the interface resistance R-b between the phosphor fillers and silicone matrix cannot be neglected. (C) 2012 Elsevier Ltd. All rights reserved.