This work aimed to study the effects of selenium nanoparticles and nicotinamide in-ovo injection on hatchability and physiological traits of broiler chicks at hatch day. A total of 500 eggs from Arbor Acres breeder hens were weighed and distributed into five treatments with four replicates for each. At day 18 of incubation, eggs of the first group were non-injected and served as control, while the 2^nd group was injected with normal saline at 0.9 % (saline group). But, the 3^rd group was injected with selenium nanoparticles (SeNPs) (20 μg SeNPs/ egg) the 4^th group was injected with nicotinamide (NAM) (300 mM NAM/ egg) and the 5^th group was injected with their mixture (20 μg SeNPs plus 300 mM NAM/ egg). The results showed that chicks of saline and mixture in-ovo injection groups had higher significant weights at hatch compared to all other studied groups. In contrast, eggs of the in-ovo NAM injected group had higher hatch of fertile egg percentage values with insignificant differences with both control and mixture injected groups. The chicks of NAM and mixture in-ovo injected groups had significantly highest WBC values compared to all other studied treatments. The chicks of SeNPs, NAM, and mixture in-ovo injected groups have significantly higher low-density lipoprotein compared to control and saline groups. This suggested that the in-ovo injection with NAM and the mixture groups used in the present study had a considerably positive effect on hatchability percentage, chick weight, relative chick weight, white blood cell count, and blood glucose level and the activity of total antioxidant capacity (TAC). In conclusion, injection of eggs in-ovo of broiler chicks with 300 mM nicotinamide/ egg and mixture between 20 μg SeNPs plus 300 mM NAM/ egg enhanced hatchability and some physiological traits for chicks.