Modified Universal Soil Loss Equation (MUSLE) is one of soil loss estimation models which has been developed based on the runoff characteristics in the event scale. However, it needs to be evaluated in the plot scale for the semi-arid rainfall events. With this aim, a field study was designed using twenty one plots. Runoff and soil loss were measured using 5-min samples under seven rainfall intensities consisted of 10, 20, 30, 40, 50 60, and 70 mm h^-1 for 60 min. Soil loss was estimated using the MUSLE based on the runoff volume (Q) and runoff peak discharge (q_p) and the values were compared with the observed values. The estimated soil loss was about 3.89 times bigger than the observed value on average. In order to improve model estimations, the power of rainfall erosivity index was modified from 0.56 to 0.62, (Q q_p)^0.62. The modification of the MUSLE model improved model efficiency (ME) from -5.5 to 0.47 and decreased the root mean square error from 0.000137 to 0.000031. This study revealed that the MUSLE overestimates soil loss from the small plots in the semi -arid regions. Therefore it is essential to calibrate runoff erosivity index using the data observed in the area. The modified MUSLE can be reliably used to predict soil loss in the small plot scale in semi-arid regions.