The results of the research were based on a field experiment conducted in 2015-2017 on an individual farm in Międzyrzec Podlaski in Poland. The aim of the study was to determine the effect of the type of biostimulants used (Kelpak SL®, Titanit®, GreenOk®, BrunatneBio Złoto®) on the total and true protein content in tubers of three edible potato varieties (Honorata, Jelly, Tajfun). Potato plants were treated three times with biostimulators (beginning of flowering, full flowering and after flowering), the control variant was potato plants without the use of biostimulators, sprayed with distilled water. Prior to the experimental harvest from all plots, tubers from 10 potato plants (excluding marginal plants) were randomly dug. The harvest was made during the technological maturity of tubers, in the first decade of September. The total protein content was determined by the Kjeldahl method, and the specific protein was separated from the non-protein compounds by precipitation with trichloroacetic acid and determined by the Bernstein method (AOAC 2006). The experiment was based on a random-split sub-plot. Genetic traits of studied varieties affected the content of crude and proper protein. The highest levels of total protein were accumulated in tubers of the Tajfun variety, and the highest content of true proteins was noted for the Jelly variety. The weather conditions in the years of the study were another factor shaping the content of total and true protein content in potato tubers. Accumulation of protein was favoured by the dry period from July to September. A large amount of precipitation – 325.4 mm – and the lowest average air temperature – 14.6°C in 2017 contributed to the reduction of total protein content in potato tubers. Tubers of plants treated with the preparation BrunatneBio Gold were characterised by the highest content of total and true protein in comparison to plants from the control variant.