This study was carried out in the poultry experimental unit, poultry production department, Faculty of agriculture, Fayoum university. It amid to study the effect of in ovo injection by selenium nano particles on body weight, body weight gain, feed intake, feed conversion, carcass traits, plasma protein constituents, plasma lipid constituents, and some blood parameters at the 7 week of age of improved Baladi chicken raised in an semi open house during the period from April to July. A total number of 525 fertile improved Baladi eggs with an average weight of 51.30g±0.81 were used. Before incubation, eggs were randomly divided into seven groups. The first group was non-injected eggs, considered as control(T1), the second group was injected into air sac with 0.1 ml sterile water with volume of 0.1 ml/egg (T2), the third group was only punctured (T3) while the fourth (T4), fifth (T5) , sixth (T6) and seventh (T7) groups were injected into air sac with consentration of 0.05, 0.075, 0.1 and 0.2 µg SeNPs respectively . All eggs were normally incubated at 37.5 ºC and 65% relative humidity in an automatic incubator. Egg injection procedure was carried out at day 10 of incubation. At the 18th day of incubation, all eggs were transferred to the hatcher and kept till hatching at 36.5°C and 80% RH. The hatched chicks from the seven groups were brooded in suitable floor pens with chopped wheat straw litter. Then Chicks were housed in galvanized wire cage batteries for 7 weeks of age. Results obtained could be summarized as follows: 1- Finally body weight, Body weight gain were significantly increased in treated groups compared by control groups. 2- Feed consumption increased but feed conversion ratio improved in selenium nano particles treatments compared by control. 3- SeNPs injection of improved Baladi chicken increased carcass%, liver% and gizzard%.