Five 2-pyridinecarboxylic acid-related compounds (1, 2 and 5-7) showed germination inhibition against the seed of Brassica campestris L. subsp. rapa HOOK fil et ANDERS at a concentration of 5.0×10^-4M. These compounds also demonstrated inhibitory activity on the growth of the root of this plant at a concentration of 3.0×0^-4M; among these compounds, 2-pyridylacetic acid (5) showed the strongest inhibitory activity, and the effect was slightly stronger than that of sodium 2, 4-dichlorophenoxyacetate (2, 4-D) used as a positive control. The amounts of chlorophyll in the cotyledons of this plant treated with these active compounds was lower than that of the control group. Four compounds (1 and 5-7) with germination inhibition also showed inhibitory activities against α-amylase and carboxypeptidase A, and 5 was the strongest inhibitor toward both enzymes.