In this paper, the effect of the hot plate welding parameters on the weld strength of 40 % calcite filled polypropylene were investigated by utilizing design of experiment and compared to talc filled polypropylene. The plate temperature and the heating time were considered as the process parameters. A mathematical predictive model of the weld strength was developed in terms of welding parameters. The results show that the mathematical model correlates well with the experimental results. The optimum welding parameters of calcite filled polypropylene are determined as 260 degrees C of plate temperature and heating time of 25 s. The welding strength of the joint welded at optimum parameters is found as 18.32 MPa. Hot plate welding efficiency of the 40% calcite filled polypropylene is observed to be higher than 40 % talc filled polypropylene material.