Availability of large number of recorded strong motion data by the Iranian strong motion Network has motivated this study to develop relations for routine determination of ML and MW from digital horizontal components of the strong motion records. The datasets is comprised of about 800 accelerograms recorded by 82 earthquakes of magnitude 4.5 and larger. For MW scale the objective technique was employed. testing variety of time windows shows that the estimated MW values are best correlated with the corresponding values reported by teleseismic data when S window durations are chosen. The regression has the form of Mwo= (0.92 ±0.08) Mwt + (0.45±0.22). Mwo and Mwt are respectively the estimated and reported moment magnitudes. The ML scale is based on the horizontal synthesized WoodAnderson seismograms. We have employed the Monte Carlo technique to evaluate -loga0 as a function of distance. Results indicate that the attenuation curve has three distinct sections. at distances less than 65 km amplitudes decay slightly less rapid than 1/r (r0.94). Between 65 and 106 km, amplitudes are approximately constant. Between 130 and 200 km, amplitudes decay at a rate that is consistent with R-0.5. Finally, the relationship between the local and moment magnitudes in Iran using strong motion data is: ML= (0.59± 0.06) MW + (2.60±0.15)

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