ABSTRACTA number of fatigue cracking experiences have been reported at the lower part of cross beam slits intersected by bulb ribs with R less than 35mm. In this study, fatigue behavior of cross beam slits with R of 40mm is investigated and effectiveness of retrofitting methods of R dressing and small size attachments, through fatigue tests using three specimens cut out from a removed bulb rib orthogonal steel deck box girder bridge. The shape and size of R dressing were determined through finite element analyses. As a result, stress concentration was higher at the upper part than the lower part of slits. By the R dressing, stress concentration moved from fillet welds to R part in the mother material. By the small size attachment, stress concentration decreased at the upper part of slits. Fatigue cracks were initiated at the upper part of R40 slits and propagated into fillet welds between the deck plate and cross ribs without retrofitting methods, while no fatigue cracks were developed with R dressing and small size attachments. After fatigue cracks were initiated, small size attachments could stop propagation, of there cracks.