In this study, the implementation of an image processing technique on Compute Unified Device Architecture (CUDA) is discussed. CUDA is a new hardware and software architecture developed by NVIDIA Corporation for the generalpurpose computation on graphics processing units. CUDA features an on-chip shared memory with very fast general read and write access, which enables threads in a block to share their data effectively. CUDA also provides a userfriendly development environment through an extension to the C programming language. This study focused on CUDA implementation of a representative optical flow computation proposed by Horn and Schunck in 1981. Their method produces the dense displacement field and has a straightforward processing procedure. A CUDA implementation of Horn and Schunck?s method is proposed and investigated based on simulation results.