An experiment was conducted to determine the effects of gibberellic acid (GA3) on growth and yield of "American Flag" leek (Allium porrum L.) grown in containers. It was found that GA3 foliar application in dosages ranging from 0 (control) to 50 ppm did not cause significant effects on growth or yield when applied seven days after transplant (four-leaf stage). However, GA3 application 21 days after transplanting (seven-leaf stage) significantly increased leaf area as well as pseudo-stem weight and diameter at rates 30, 40 and 50 ppm, although no significant effects were detected on plant height and pseudo-stem length. These results suggest that yield and quality of "American Flag" leek can be enhanced by GA3 application in the seven-leaf stage.