Local scouring is one of the most important causes of bridge failure. Therefore, there is an interest in finding reliable ways to control and reduce local scour depth and, thereby, requisite pier embedment depth. Countermeasures for local scour at bridge piers can be grouped in two categories: Armoring devices and flow-altering devices. An accepted engineering method to deal with pier scour problems is to place riprap material around the pier foundation. The scour-reduction of riprap has been the topic of scientific investigations. The effect of riprap on pier groups is not studied by earlier researches. The scour hole around group piers is affected by factors which are not valid for single pier. Therefore study in this field is necessary. For group piers (aligned with the flow), reinforcement and sheltering are additional parameters, which affect the depth of local scour. Furthermore, the group effects will alter with changes in pier spacing. The present study examines using of riprap for reduction of local scour in pier group. The results of the experiments were compared with data from present study and earlier studies on single pier with riprap. The models consist of two and three circular-shaped piers in line with diameter of 0.02 m and pier spacing of twice and four times the pier diameter. Four uniform sediments with median diameters d 50 = 2.86, 3.67, 4.38 and 5.18 mm, were used as riprap material. The riprap layer were installed at the same, above and below the surface of the streambed. The results showed that instability depth in group pier was lower than single pier because of the sheltering effect. The reduction in instability depth at riprap placed below is found to be as much as 8.33% for biggest riprap and 6.1% for smallest riprap. The riprap stability for three piers in line is more than single pier and two piers. The stability number for riprap with median diameters d 50 = 2.86 and 5.18 mm is 3.29 and 2.38, respectively. According to the results, stability number increased with increasing pier spacing. From the results, riprap placed below the surface of the streambed has the highest stability, riprap stones placed above the surface of the streambed have the lowest stability, and the third ones have the value between previous ripraps. The effect of wake vortices formed at the downstream side of group piers was decreased. Therefore the cover of riprap layer at downstream of group piers was decreased as compared with single pier. The reduction in cover of riprap layer was about 60% .