Motivated by the lack of qualitative analytical parameters to characterize wastewater and wastewater treatment process effluents, the present work investigated a dissolved organic matter separation technique supplemented by conventional analytical techniques (TOC, UV absorption) to better describe the nature of dissolved compounds. This technique based on gel permeation was first optimized for its application to urban wastewater characterization in terms of organic compound molecular weight distribution. The technique was then used to qualitatively compare two different wastewater treatment processes. The comparison showed markedly different removal efficiencies on each class of compounds defined by a molecular weight range and demonstrated that this technique could be used to better characterize treatment processes.