The object of the laboratory experiment was to investigate the effect of aqueous extracts of dried St. John’s Wort (Hypericum perforatum L.) in concentrations of 2%, 5% and 10%, and fresh parts of this plant, in concentrations of 10%, 20% and 30% on feeding of larvae of Colorado potato beetle (Leptinotarsa decemlineata Say) at L3 and L4 stages. We examined the mass of eaten potato leaves treated with different extracts after 24, 48 and 60 hours from the start of the experiment. Additionally, reactions of adult potato beetle individuals to the scent of the above mentioned plant was tested with the use of an olfactometer. Aqueous extracts from St. John’s wort exhibit inhibitory effect on feeding of potato beetle larvae at a concentration of at least 5% and 10% for dried plant and 20-30% for fresh plant weight and the effect is stronger for L3 larvae than L4 larvae. However, the comparatively low values of the absolute deterrence index suggest limited possibility to use aqueous extracts from the plant for the inhibition of potato beetle larvae feeding. Tests with the use of olfactometer did not exhibit a deterrent reaction of aromatic substances from St. John’s wort to adult individuals of potato beetle (both females and males).