The study was undertaken to study a relationship between the changes of some parameters of the biochemical and mineral composition of different plants, such as rape, pods, and lentil, and the levels of soil radiation pollution, by using the conventional methods. Radioactive pollution of dark-grey forest soils was found to cause a change in the biochemical composition of plant seeds even at the level of cesium 137 (137Cs) within the present temporary permissible levels (TPL) (600 Bq/kg): there were elevated concentrations of salts of potassium, phosphorus, ammonia nitrogen, catechols, sucrose, and some amino acids. With the radioactive cesium level exceeding the TPL, biochemical changes in the seeds depended on the species of the plants: in the rape seeds, the additional formation of sucrose and amino acids continued, but less intensively than with its lower radiation; the pod beans were significantly positively correlated with the increasing amounts of catechols.