Counterconditioning (CC) is a form of retroactive interference that inhibits expression of learned behavior. But similar to extinction, CC can be a fairly weak and impermanent form of interference, and the original behavior is prone to relapse. Research on CC is limited, especially in humans, but prior studies suggest it is more effective than extinction at modifying some behaviors (e.g., preference or valence ratings) than others (e.g., physiological arousal). Here, we used a within-subjects design to compare the effects of aversive-to-appetitive CC versus standard extinction on two separate tests of long-term memory in human adults: implicit physiological arousal and explicit episodic memory. Participants underwent Pavlovian fear conditioning to two semantic categories (animals, tools) paired with an electric shock. Conditioned stimuli (i.e., category exemplars) from one category were then extinguished, while stimuli from the other category were paired with a positive outcome. Participants returned 24-h later for a test of skin conductance responses (SCR) to the conditioned exemplars, as well as a surprise recognition memory test for stimuli encoded the previous day. Results showed reduced SCRs at a test for unique stimuli from a category that had undergone CC, relative to stimuli from a category that had undergone standard extinction. Additionally, participants selectively remembered more stimuli encoded during CC than extinction. These results provide new evidence that aversive-to-appetitive CC, as compared to extinction, strengthens memory for items directly associated with a positive outcome, which may provide stronger retrieval competition against a fear memory at test to help diminish fear relapse.