The recovery program for the endangered June sucker (Chasmistes liorus) relies on population augmentation to overcome recruitment deficits. Successful recruitment of artificially propagated individuals is affected by release timing, release size, and rearing techniques. We examined the effect of release timing and release size (total length [TL] and a relative condition factor [W_r]) on recruitment probability of hatchery-reared June sucker (Utah Division of Wildlife Resources Fisheries Experiment Station [FES]) and captive-reared June sucker (Red Butte Reservoir [RBR] refuge population) stocked across multiple years. Because source and year effects were confounded, we assessed the probability of recruitment individually for each major stocking event (i.e., source × year combination). Successful recruitment occurred if an individual was recaptured or detected at least once during annual spawning runs up Utah Lake tributaries. For stocking events from RBR, probability of recruitment was highest in individuals stocked during spring and early summer but decreased as summer progressed. No difference existed between spring and fall stocking events. June sucker from the FES stocked in October had lower overall probability of recruitment than those stocked in August. The relationships between recruitment probability and TL and W_r for stocking events from RBR were hump shaped, with peaks at approximately 375 mm TL and 100%, respectively. For FES individuals, a positive relationship existed between recruitment probability and TL for individuals stocked during August only; no relationship existed between the recruitment probability and W_r. Release timing and release size affected the recruitment success of captive-reared June sucker; therefore, recovery plans should incorporate these factors in augmentation efforts to maximize augmentation efficiency and success.