There are various kinds of methods to build-up L-type sections as shown in Fig. 1. L2-and L4-type webs are commonly used in ship structures. Especially, L4-type webs are recently used at engine room webs, transverse rings on top side tanks of bulk carriers and deck transverse webs of cargoes etc. bscause of easiness to built. But, the section of L4-type webs are unsymmetrical and thier top sides are left as cut by gas. An experimental investigations into their fatigue strength were made in this paper. The fatigue strength of L4-type webs is compared to that of T-type web which are usually used at webs or girders. The conclusions obtained are as follows: (1) The fatigue strength of L4-type webs is approximately same as that of T-type webs. (2) The effect of gas-cut edges on the fatigue strength of L4-type webs can be estimated from that of the mother plate. (3) The fatigue strength of the welded portion can be estimated from that of the parallel parts with the aid of Neuber's approximate equation. (see equation (4))