The influence of magnetic field stimulation (MFS) on plants is a subject of intense research. The influence of MFS on plants varies depending on its intensity, time of exposure, and form of application. Weak MFS has beneficial effects on physiological and biochemical processes in plant tissues. Lupins (Lupinus spp.) are economically and agriculturally important plants used mainly in livestock feeding or in human consumption. The effects of a stationary magnetic field (130 mT) on the mitotic activity and selected biochemical parameters of lupin (Lupinus angustifolius L.) were evaluated. Nonexposed plants were used as the control. It was noted that the stimulation of plants with a 130-mT magnetic field favored the aboveground parts of the plants, which was manifested by an increase in the average length and fresh weight of shoots and an increase in the photosynthetic pigment content. However, guaiacol peroxidase activity decreased in shoots after their exposure to 130-mT MFS. The development of roots was at the control level. Moreover, an increase in the total protein content in both shoots and roots was observed after the MFS.