Gender mainstreaming has been celebrated as a new policy strategy for change in gender relations. However, its transformative potential seems to be lost in the process of implementation. The aim of this article is to evaluate the policy effectiveness of gender mainstreaming and its ability to bring about change in gendered social structures and practices. Previous research has focused on gender mainstreaming as a policy strategy. This article provides a new perspective on the problems of implementation by approaching gender mainstreaming from an organizational perspective. Gender mainstreaming takes place in certain organizational contexts, implemented by local actors. This article reveals the practices of implementation in the Finnish state administration, specifically in the Ministry of Defence. The analysis is based on a discursive reading of thirteen group and individual interviews collected in the Ministry of Defence in 2012. The article pinpoints two interlinking problems concerning implementation of gender mainstreaming on the organizational level. First, the state officials, who should implement gender mainstreaming, do not have enough information to do so successfully. Second, there is resistance toward gender mainstreaming on the organizational level. This article suggests that negotiations about gender, gender equality and gender mainstreaming as complex issues concerned with social power relations should be included in the process of implementing gender mainstreaming.