RNAi agents for inhibiting the expression of the alpha-1 antitrypsin (AAT) gene, compositions including AAT RNAi agents, and methods of use are described. Also disclosed are pharmaceutical compositions including one or more AAT RNAi agents together with one or more excipients capable of delivering the RNAi agent(s) to a liver cell in vivo. Delivery of the AAT RNAi agent(s) to liver cells in vivo inhibits AAT gene expression and treats diseases associated with AAT deficiency such as chronic hepatitis, cirrhosis, hepatocellular carcinoma, transaminitis, cholestasis, fibrosis, and fulminant hepatic failure.