Organic solar cells (OSCs) have been extensively studied and significant improvements have been demonstrated in recent years. Along with the excitement in technology development, the accurate measurement of OSCs has become critical for the healthy development of this promising technology. The limited absorption and spectral response of organic based solar cells could lead to significant derivation in solar cell measurement. In this paper, we will discuss several issues in the measurement of organic solar cells, including spectral mismatch factor, elimination of the mismatch by proper selection of reference cell, external quantum efficiency testing, device area issue etc. Results on both polymer based bulk hetero-junction solar cell and small molecule based solar cell will be presented.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.