While teacher-to-teacher knowledge-sharing is promising for professional learning and improving teaching quality, it lacks integration and timeliness in schools because teachers are usually weak at knowledge-sharing. Despite this weakness, principals as knowledge-sharing leaders can make a difference. There is still limited research about this promising leadership role. One possible reason might be the deficiency of a focussed assessing scale. This study was conducted to develop and validate a scale in Tehran, Iran. To this end, four consecutive sub-studies, including inductive item-pool generation, deductive item-pool generation, content validation, and construct validation, were conducted, and the Knowledge-Sharing Leadership Scale was introduced consequently. The KSLS comprised five dimensions: role-modelling, trust-building, setting expectations, creating a knowledge-sharing-driven environment, and encouraging teachers. It is expected that the KSLS could serve as a practical means for promoting relevant research and practice. Directions for future research and implications are discussed.