In the assembly stage of ship construction, gap is often produced between the prepared edges of joints owing to welding deformation, etc. Especially, in the case of Tee-type fillet welded joints, to establish effective joining methods is an important problem. The effective method should be discussed from the view points of efficiency in procedure and strength of the joint. Today, the following three methods are used for welding of joints with gap : by increasing the leg length, by welding with bevel preparation, by inserting a liner into the gap. Sufficient strength of joint should be guaranteed regardless of the amount of the gap and the kind of treatment. In this report, the effect of the treatment for the gap on static and fatigue strength for Tee-type fillet welded joints were investigated. As the amount of penetration influences the strength of the joint, the relation between the amounts of penetration and the gap was studied by experiments. The counterplan of the treatment considering the strength and the welding procedure was then discussed and the following conclusion was obtained : (1) In the case, where the gap is smaller than 3 mm, the joint with the rule leg length shows sufficient strength. (2) If the gap g is greater than 3 mm, additional leg length, A is required as follows : A = g -3 (mm) (3) If the gap is larger than 5 mm, a piece of liner should be put into the gap. The liner breadth, B , must satisfy the following condition : t +2 R +10≤ B ≤ 3 h (mm) where, h : thickness of liner t : thickness of base plate R : rule leg length In this case, the rule leg length furnishes sufficient strength of the joints.