In this study, non-load-carrying fillet welded joints fabricated using EH grade-steel are evaluated with the structural stress approach. The thickness effect was investigated by a study on welded steel joints with thickness ranging from 25 to 80mm. As-welded joint for main plate thickness of 25 to 80mm, the fatigue strength is reduced gradually. On the other hand, in case of main plate thickness of 25 to 80mm, the structural stress concentration factor increases gradually. As a result, for structural stress approach, thickness effect is not required for correction. Based on these results, a new evaluation fillet welded joint for fatigue design purposes has been proposed FAT 125.