Determining the maximum credible earthquake (Mmax) for seismic sources has always been considered one of the most important input parameters of seismic hazard assessment (SHA). Due to the lack of data records, applying various statistical methods is not practical in seismic sources that are as large as a fault or a fault segment; Therefore, the alternative methods, such as empirical relationships, should be used. In this paper, using the MATLAB program and combining several methods, including empirical methods that provide the maximum earthquake in terms of length (MRLD) and fault area (MRA), the use of scalar moment (M0), Aspect Ratio (AR) method and also the maximum observed earthquake (M_max^obs) of the fault, the Mmax of the Sabzevar fault has been calculated. The results of this study shows the Mmax for Sabzevar, Esferayen, Neyshabour, Torbat-e-jam, Kelidar, Baghan 7.1, 7.0, 7.2, 7.4, 6.9,7.1 respectively.