Cannabis is one of the oldest cultivated plants in East Asia, grown for grain and fiber as well as for recreational, medical, and ritual purposes. It is one of the most widely used psychoactive drugs in the world today, but little is known about its early psychoactive use or when plants under cultivation evolved the phenotypical trait of increased specialized compound production. The archaeological evidence for ritualized consumption of cannabis is limited and contentious. Here, we present some of the earliest directly dated and scientifically verified evidence for ritual cannabis smoking. This phytochemical analysis indicates that cannabis plants were burned in wooden braziers during mortuary ceremonies at the Jirzankal Cemetery (ca. 500 BCE) in the eastern Pamirs region. This suggests cannabis was smoked as part of ritual and/or religious activities in western China by at least 2500 years ago and that the cannabis plants produced high levels of psychoactive compounds.