The lateral torsional buckling of coped steel I-beams was investigated extensively by a number of researchers. Design recommendations have been proposed by Cheng and Yura. They proposed a set of interaction equations to evaluate the elastic lateral torsional buckling capacity of coped steel I-beams based on the interaction of the lateral torsional buckling capacity of the coped (tee-section) and the uncoped regions. However, these interaction equations may not be appropriate for sections with a small ratio of cope length to web depth of the tee-section because local web buckling of the tee-section may occur. In this paper, modified interaction equations based on an analytical study of tee-sections are proposed with improvement over Cheng and Yura’s interaction equation. For symmetrical loading, the use of the equivalent moment coefficient Cb in Cheng and Yura’s design interaction formula for calculating the critical moment of coped I-beams may produce non-conservative results. Subsequently, a modified interaction formula is proposed.