Mengen lignite was pyrolyzed in a thermobalance apparatus at atmospheric pressure. The effects of heating rare and particle size on the pyrolysis kinetics were investigated. Experiments were conducted at nonisothermal conditions with a hearing rate range of 10-90 K/min in the pyrolysis temperature interval of 298-1173 K under an argon atmosphere. Two particle size ranges were examined: 125 > D-P > 63 and 63 > D-P > 44 mum. Although some differences were obtained in TG/DTG curves of the lignite samples at different heating rates, almost constant relative yields of 45 and 40% of the total volatile matter were calculated from 673 to 873 K for the linear segments of the TG curves of the larger and smaller size particles, respectively. Thermogravimetric data were analyzed by reaction rate model assuming past-order kinetics, and kinetic parameters were determined. Lower activation energies were calculated at higher hearing rates. Minimum activation energy was obtained as 22.4 kJ/mol at the heating rare value of 90 K/min with 63 > D-P > 44 mum size lignite panicles. It appears to be the lowest one when compared to those obtained from the literature.