According to the study, 31% of the world's 1,480 cactus species were under pressure from human activity, such as illegal trading, agriculture and aquaculture as well as land-use change.
"The results of this assessment come as a shock to us," said lead author Barbara Goettsch, co-chairwoman of the IUCN's Cactus and Succulent Plant Specialist Group.
"We did not expect cacti to be so highly threatened and for illegal trade to be such an important driver of their decline."
The assessment reported that the illegal trade of live plants and seeds for the horticultural industry and private collections, as well as their unsustainable harvesting, affected 47% of threatened species.
These plants which have evolved to cope with the harsh conditions found in arid landscapes are native to North and South America, with exception of one species that is native in southern Africa and South Asia.