Surface colour of cashew kernels is one of the physical attributes used to determine the quality in cashew processing industry. Although manual grading of cashew kernels is followed in the Indian cashew processing system, the mechanised colour grading machine is gaining importance due to shortage of skilled man power. In the study a high speed colour sorter suitable for cashew kernel is evaluated for its performance in terms of operational capacity and purity index. Certain grades of whole kernel and broken kernel grades with different proportions are used. Estimation of the operational capacity revealed significant differences among the grades investigated,  with higher value of 156 kg h^-1 for the largest kernel (WW 210) and 52 kg h^-1 for the smallest kernels (BB). Purity index showed a dependence on kernel size and was influenced by proportion of the kernels. Cost economics indicated that mechanical grading saves 40% of the total cost incurred for manual grading of cashew kernels.