Volatile organic compounds (VOCs) are major gas-phaseindoor air pollutants, and filtration is one of the promisingmethods to control indoor VOC concentration levels. Anadsorption technique is commonly used for filtration of VOCsusing adsorbents such as activated carbon. Unlike a particlefiltersystem, the applications of gas-filter systems have notbeen widely studied, and standards for the evaluation of gasfiltersystems do not exist. As groundwork for standards development,this study proposes an experimental method that canevaluate the performance of gas filters in removing VOCs. Fourdifferent fibrous, activated carbon filters were tested using adynamic closed-loop test system with toluene as a representativeVOC. Since in the proposed test system the level of VOCsin the supply air to the filter will increase as filter efficiencydeclines, the proposed test system is more similar to real-lifefilter applications than dynamic open-loop tests, where theload is always constant. The effects of injection rates, flowrates (or residence time), and the number of filter layers (orthickness) on the filter performances were investigated.