First, this study aimed to evaluate the effects on hatchability of in ovo supplementation of beta alanine (βA). Second, it assessed the effects on performance, meat quality and serum constituents of broiler chickens of βA injection in ovo and of supplementation with βA in feed for the first seven days after hatching. For this purpose, 960 fertilized broiler chicken eggs were distributed to hatchery trays in four treatment groups with six replicates on day 17 of incubation. The treatment groups consisted of eggs that were not injected (T1; negative control), injected with sterile solution with 0.9% salt (T2; positive control), injected with in ovo 1% βA solution (T3), and not injected, but with chicks were fed 1% βA for the first seven days after hatching (T4). Upon hatching, chicks from T1, T2, and T3 were fed commercial starter feed. All treatments were assessed with six replicates of 28 birds (14 females and 14 males) throughout the grow-out period. As a result of this study, T3 increased hatchability, yolk-free hatching weight and chick quality, and decreased yolk weight and feed access time at hatch. Both T3 and T4 improved carcass yield and meat quality, and T3 increased serum total antioxidant status at 42 days afer hatching. The results demonstrated that in ovo βA feeding improved hatching characteristics, and βA administration in ovo or in feed improved carcass yield and meat quality without affecting growth performance.