Eleven compounds from indigenous cinnamon (Cinnamomum osmophloeum) leaf essential oil were identified by GC-MS and the dominant constituent was trans-cinnamaldehyde (79.85%). The toxicity of leaf essential oil and trans-cinnamaldehyde were then determined to study their effectiveness in controlling the red imported fire ant, Solenopsis invicta Buren. The results of the toxicity tests indicated that both the indigenous cinnamon leaf essential oil and trans-cinnamaldehyde had an excellent inhibitory effect in controlling the red imported fire ant. The LT50 values for both 2% leaf essential oil and 2% trans-cinnamaldehyde after open exposure were 105.0 min and 32.2 min; after close exposure were 18.5 min and 21.2 min, respectively. (C) 2007 Elsevier Ltd. All rights reserved.