Within the last decade several studies have been conducted to evaluate the geotechnical properties of bottom ash obtained from electric utilities burning pulverized coal amended with admixtures such as clay, bentonite, and lime. Most of these studies concentrated on evaluating strength and stiffness characteristics of the mixtures. Because of the high volume change characteristics of bentonite and clay, improper and/or excessive use of these admixtures can impart significant swelling characteristics to the mixtures. This study was conducted to evaluate the swelling properties of two bottom ash-bentonite mixtures compacted at various initial moisture contents. Results from this detailed investigation show that the swelling potential increased with the increase in bentonite content and decreased with the increase in initial moisture content. Mixtures with 20% bentonite were observed to have volume change characteristics that may not be suitable for some lightly loaded structures. Mixtures with 15% bentonite; compacted at initial moisture contents of 18% or higher; were observed to have less than 4% free swell, whereas for mixtures compacted at an initial moisture content of 16% or. lower, the percent increase in free swell was observed to be greater than 7%.