Abstract: An experiment was conducted to investigate the effect of in ovo L-carnitine injection at three incubational ages on hatchability of broiler breeders and post-hatch performance. Four doses of L-carnitine (0.0, 4, 8 and 12 mg/100 μL) were injected into fertile eggs at days 14, 16 and 18 of incubation. Hatched chicks were individually weighed and fertile hatchability was calculated. Birds were kept in batteries and fed common starter and grower diets. Means of weight gain, feed intake and feed conversion were estimated. Mortality was also monitored. A slaughter test was made to evaluate the relative weights of carcass yield, front and hind parts and the edible organs. No deaths occurred during a 7-week feeding trial. Hatchability was unaffected by the injected dose of L-carnitine but it significantly improved when eggs were injected on day 14 of incubation compared with those injected on days 16 or 18. Although, total feed intake of chicks was not affected by in ovo L-carnitine injection, cumulative weight gain was positively affected. Birds hatched from eggs that were injected with L-carnitine at 8.0 or 12.0 mg/100 μL achieved significantly better feed conversion compared with the control group. Injection with 12.0 mg/100 μL positively affected the percentages of front parts but decreased those of liver and gizzard and had no effect on other traits examined. It is concluded that in ovo L-carnitine injection is beneficial for hatchability on day 14 while its injection at 8.0 mg/100 μL on day 16 of incubation is advantageous to subsequent performance.