Green roofs are increasingly being used in the United States to mitigate the negative effects of impervious surfaces on aquatic ecosystems. Though performance of these systems varies with climate, little research has been conducted in the Southeastern U.S., and no prior research has been conducted in Mississippi. An experiment was conducted to determine the effect of soil depth and roof slope on the stormwater retention of green roofs in Mississippi’s hot, humid climate. Simulated roof platforms were constructed to investigate two soil depths and two slopes, each replicated three times and planted with four species of Sedum. The green roof platforms significantly reduced runoff depth when compared with total rainfall depth. Soil depth and slope both significantly affected retention, with higher retention seen with increasing soil depth and lower retention seen with increasing slope. These results indicate that green roofs can be an effective tool to reduce runoff in Mississippi.