This study aimed to investigate the effect ofin-ovo injection with probiotic on hatchability traits, growth and physiological response of post-hatch Sinai chicks. A total of 600 fertile eggs at the initial of the 18^th day of incubation were used and divided into 4 equal treatments (150 eggs per each). The experimental groups of eggs were arranged as follows, the first group as a control negative (un-treated), the second group as a control positive (injected in air sac with 0.3 ml/egg of sterile distilled water), the third and fourth groups injected with 0.3 ml/egg solution of sterile distilled water contained 1.0   and 2.0 g probiotic per one liter, respectively.  Hatched chicks were reared up to 12 wks of age, then growth and some physiological parameters were estimated through the experimental period. Results indicated that in- ovo injection eggs by probiotic with 1.0 or 2.0 g / L result in improve hatchabilityand decrease embryonic mortality percentages. Both body weight gain and feed conversion ratio were significantly improved as a result of in-ovo injection with 1.0 g probiotic/L than the negative control during the overall experimental period after hatch (0-12wks of age). Relative weights of some giblets and organs were increased as a result of in-ovo injection with probiotic as compared with negative control with or without significant effect. Growth and physiological response of hatched Sinai chicks. Therefore, in-ovo injection by probiotic with 1.0 or 2.0 g / liter at 18^th day of incubation period could be used to improve hatching and subsequent growth performance of hatched Sinai chickens.