In the dating studies of old samples using the Infrared Stimulated Luminescence (IRSL), the validity of the curve-fitting employed is of critical importance. So, in this study, a new fitting procedure was suggested for obtaining the age of the old geological sample. IRSL technique was applied using multiple-aliquot procedure to feldspar isolated from sample. The paleodose results obtained, using linear and polynomial fitting, Were (67.98 +/- 2) Gy, (30.49 +/- 2) Gy and 322.03 Gy from the suggested fitting procedure. After application of this procedure the age was found to be 551.4 ka.