The Clean Development Mechanism (CDM) is one of important mechanisms to assist in achieving the mitigation target assigned in the Kyoto Protocol. However, the additionality of small-scale hydropower project activities has been a debated issue in the Parties. The method for assessing the additionality is the core for the eligibility. On the basis of Shiba hydropower CDM project, this thesis discusses the types and their essential implications of the additionalities of small-scale hydropower CDM project activities, and the rationality and feasibility of the methods for assessing additionalities, hoping to the contribution to preparation and implementation of small-scale hydropower CDM project activities in China. (C) 2010 Elsevier Ltd. All rights reserved.