This study investigated the role of offline consolidation, specifically sleep, in transforming memories strengthened by retrieval practice into stable long-term representations. Forty-eight participants learned weakly associated Chinese word pairs via restudy(RS), retrieval practice with feedback (RP), and retrieval practice without feedback (NRP). After encoding, a nap group slept while a wake group remained awake. Recall was tested after 90 min and 24 h. Critically, only for RP items did the nap group show significantly less forgetting (i.e., a reduced recall change rate) than the wake group. Furthermore, the RP recall change rate correlated positively with sleep-specific neurophysiological markers (fast spindle density and fast spindle-ndPAC coupling). These findings demonstrate that initially labile memories formed by RP undergo offline, sleep-dependent consolidation (involving neural replay indexed by spindles), integrated with online processes, to achieve long-term stability.