There is increasing evidence that projected near‐future carbon dioxide (CO 2 ) levels can alter predator avoidance behaviour in marine invertebrates, yet little is known about the possible effects on predatory behaviours. Here we tested the effects of elevated CO 2 on the predatory behaviours of two ecologically distinct cephalopod species, the pygmy squid, Idiosepius pygmaeus, and the bigfin reef squid, Sepioteuthis lessoniana. Both species exhibited an increased latency to attack and altered body pattern choice during the attack sequence at elevated CO 2 . I. pygmaeus also exhibited a 20% decrease in predation rate, an increased striking distance, and reduced preference for attacking the posterior end of prey at elevated CO 2 . Elevated CO 2 increased activity levels of S. lessoniana comparable to those previously shown in I. pygmaeus, which could adversely affect their energy budget and increase their potential to be preyed upon. The effects of elevated CO 2 on predatory behaviours, predation strategies and activity levels of cephalopods reported here could have far‐reaching consequences in marine ecosystems due to the ecological importance of cephalopods in the marine food web.