The paper presents research on the impact of three organic fillers from renewable sources, i.e. ground wheat bran, pumpkin seed husks and peanut shells, constituting production waste of the food industry, on selected mechanical and thermal properties of composite injection moldings based on LDPE. The basic strength properties were tested in a static tensile test, hardness and heat deflection temperature, Vicat softening point, and the microscopic structure of the obtained polymer compositions was analysed. The tests were carried out with a different mass content of fillers of 0, 5, 10, 15 and 20% and variable size of filler grains. Samples for testing were obtained in the injection molding process. An increase in the Young’s modulus and hardness as well as a decrease in the remaining tested strength properties along with an increase in the filler‘s share content were found.