AbstractCocaine‐experienced Wistar and Wistar Kyoto (WKY) rats received four daily repeated forced swim stress sessions (R‐FSS), each of which preceded 4‐hour cocaine self‐administration sessions. Twenty‐four hours after the last swim stress, cocaine valuation was assessed during a single‐session threshold procedure. Prior exposure to R‐FSS significantly altered cocaine responding in Wistar, but not WKY, rats. Behavioral economic analysis of responding revealed that the Wistar rats that had received R‐FSS exhibited an increase in the maximum price that they were willing to pay for cocaine (Pmax). Pre‐treatment with the long‐lasting kappa opioid receptor (KOR) antagonist norbinaltorphimine prevented the stress‐induced increase in Pmax. Thus, R‐FSS exposure had strain‐dependent effects on cocaine responding during the threshold procedure, and the stress effects on cocaine valuation exhibited by Wistar, but not WKY, required intact KOR signaling.