The knowledge of plants interactions is used for their better protection and cultivation. The aim of this study was to determine the influence of alcoholic extracts from the leaves of the common sunflower (Helianthus annuus) on selected physiological parameters of plants of white mustard (Sinapis alba ‘Barka’). The seeds germination, the growth, the fresh and dry masses of plants grown from seeds and germinated on the sunflower extracts and plants watered by H. annuus extracts during the growth phase were studied. In the growth phase, the fresh masses of all organs were increased on 5 % extract, however significantly decreased on 10 % extract. The dry mass of S. alba was not significantly changed. In the germination phase, much less changes of these parameters were revealed. In general, extracts from H. annuus leaves inhibited germination of S. alba seeds, but stimulated growth of plants in case of application of 5 % concentrations during the germination phase and inhibited their growth in case of application of 10 % concentrations during the growth phase.