When classing cotton fiber quality, the results are governed by three sets of conditions: 1) production conditions, which may potentially be heterogeneous (variety, soil, climate, etc.); 2) ginning conditions at each ginning step, which have a positive or negative impact on final fiber quality. 3) testing conditions in the testing and classing laboratory. Our objective was to develop a way of measuring the specific impact on fiber quality of ginning operations alone, which therefore cannot be deduced easily from classing results. A sampling and testing protocol was tested in Mali in four industrial ginning mills while processing seed-cotton modules over a cotton cropping season. During the ginning of each module, samples were taken at four stages: seed-cotton samples before and after seed- cotton cleaning, and fiber samples before and after lint-cleaning. To obtain a reference ginning, a micro-gin was used to gently process seed-cotton samples. The resulting fiber samples, as well as the corresponding fiber samples collected downstream in the industrial ginning process, were characterized within a single randomized design in two blocks including controls every twenty samples. The fiber quality results thus made available at four stages of the ginning process were used to estimate the impact of each step, as well as the overall impact of ginning on the fiber quality characterization results. When significant overall ginning impacts were detected, the proposed protocol helped in finding the ginning step that lay behind fiber quality degradation, independently from the production and characterization sources of variations in classing results. Some technical and technological developments are still necessary for applying this protocol.