Plant growth regulator is an essential pesticide to date while the available active ingredient is not well understood unlike fungicide, insecticide and herbicide. This study was aimed to evaluate a new chemical class of plant growth regulator, and the total of 92 benzene derivatives were screened for their germination and early stage of the root growth regulation on Brassica campestris. Thirty benzaldehydes, nine acids, one amide, and one ester showed potent root growth inhibitory activity (>70 % inhibition) while only salicylaldehyde showed potent germination inhibition (IC50 = 81.2 mg/L) suggesting that benzaldehyde was a key module candidate for the growth inhibition. Benzaldehydes were further evaluated for root growth inhibition. 2,3-Dihydroxybenzaldehyde and salicylaldehyde showed IC50 values of 8.0 and 83.9 mg/L, respectively. On the other hand, salicylaldehyde, and 2,4,5- trihydroxybenzaldehyde were found to have root growth promotion effects less than 10 mg/L. This result suggests that the benzaldehyde is a new class candidate for plant growth regulator.