Buildings occupants are exposed to several hundreds of pollutants in indoor environments. The utilization of in-duct ventilation filters is a promising technology in reducing the level of pollutants from indoor air. As of today, the removal performance of these filters is not clearly known. The major goal of this study is to develop an experimental method to measure the performance and service-life of full-scale in-duct Granular Activated Carbon (GAC) ventilation filters for the removal of multiple Volatile Organic Compounds (VOCs).  In this study, two sets of experiments were carried out. In the first set, the removal performance of four full-scale GAC filters with various media bed depths was measured for toluene removal. From obtained data, the applicability of the Wheeler-Jonas model in predicting the service life of full-scale GAC filters was studied and limitations were discussed.  In the second set of experiments, a 5cm-filter was tested with a mixture of representative VOCs consisting of toluene, p-xylene, n-hexane and 2-butanone. The objective was to improve understanding of the behavior of full-scale GAC filters in the adsorption of multiple VOCs. The results showed the removal performance is influenced by the physical properties of VOCs. The filter showed the highest performance in removing the p-xylene followed by toluene, n-hexane and 2-butanone. This ranking is positively correlated to the molecular weight of VOCs. VOCs competed for adsorption on the carbon surface where lighter VOCs were displaced by heavier compounds. The results showed due to the competitive adsorption, the breakthrough time of toluene in the mixture gas test had significantly decreased in comparison to the toluene breakthrough time in the single gas test.