The aim of this study was to determine the effect of biostimulators: Kelpak, Asahi SL and Goëmar Goteo on some biochemical parameters-proline and MDA concentration in leaves and florets of Monaco F1cultivars of broccoli grown under field conditions. Biostimulators applied in the experiment caused changes of some biochemical parameters in the plants. Kelpak and Goëmar Goteo significantly increased the oxidative stress parameters like the concentration of proline and malondialdehyde in leaves and florets of broccoli cultivar Monaco F1. Although, Asahi SL affected the content of chosen biochemical parameters although not seriously.