Experimental and theoretical studies on the distribution of residual stresses in butt-welded joint were performed in this research. The details of distribution of strain change due to welding and also that of elastic strain release occured by cutting after welding were measured by Gunnert's apparatus for residual stress measurement. General view of specimen and measuring points are shown in Fig. 1. Experimental results are shown in Figs. 3 to 9. Theoretical investigations upon the distribution of residual stress were also tried, and a new approximate method to calculate the distribution of residual stress was suggested. Elastic dislocation occured by transverse shrinkage and plastic deformation locally produced arround the welded zone are the two main origins of residual stresses in butt-welded joint. Distribution of residual stress due to elastic dislocation can be calculated as a problem of elasticity, however, it is very difficult to estimate the distribution of residual stresses caused by plastic deformation occurred in the region near the weld zone, as these deformations are caused by complicated change of stress during heat cycle due to welding. An attempt was, therefore, made to estimate the stress distribution due to plastic deformation locally concentrated near the weld. The method of analysis attempted in this study is quite resembled to that treated in the “boundary layer” theory in aerodynamics. The calculated stresses were compared with experimental ones, as shown in Fig. 8, and it was proved that this theory is quite acceptable for the estimation of stress distribution in butt-welded joint.