This report describes an experimental investigation on the frictional resistance of steel plates, and the slip factor of riveted joints. Tests were conducted mostly on specimens of bolted joints, so as to find out a correlation between the frictional resistance and clamping forces in the joints. The results obtained from this series of tests are as follows : 1) The friction coefficient (statical) of mild steel plates as rolled was approximately equal to 0.3. 2) Major slip load for a lap joint was about 0.6 times the clamping force where panheaded rivets were used, whereas about 0.3 times in the case of countersunk headed rivets. 3) Riveted joints subjected to a tensile force showed a minor slip at a load about 0.4 times the major slip load. After exceeding the major slip load they continued carrying load with a constant rate of displacement defined as the slip factor until reaching a plastic deformation of the specimen. 4) The slip factor depends mainly on thickness of plate, diameter and shape of rivet and fitness between rivet and rivet hole. 5) An approximate formula for the determination of the slip factor was obtained.