The in-plane thermal conductivity of cellulose nanocrystal (CNC) - poly(vinyl alcohol) (PVA) composite films containing different PVA molecular weights, CNC loadings and varying order parameters (S) were investigated as an eco-friendly, renewable and sustainable alternative to commonly used petroleum-based polymeric materials for potential application in thermal management of flexible electronics. Isotropic CNC-PVA bulk films with 10-50 wt% PVA solid loading showed significant improvement in thermal conductivity compared to either one component system. Further, anisotropic composite films exhibited in-plane thermal conductivity as high as similar to 3.45 W m(-1) K-1 in the chain direction, which is higher than most polymeric materials used as substrates for flexible electronics. Such an improvement can be attributed to the inclusion of PVA as well as to a high degree of CNC orientation. Further, a theoretical model was used to study the effect of CNC arrangement (both isotropic and anisotropic configuration) and interfacial thermal resistance on the in-plane thermal conductivity of the CNC-PVA composite films. In order to demonstrate an application for flexible electronics, thermal images of a concentrated heat source on both neat PVA and CNC-PVA composite films were taken that showed the temperature of the resulting hot spot was lower for the composite films at the same power dissipation.