This research aims to study the effect of the Cordyceps militaris supplement in the feed on the Physiological Performance and Quality of Eggs of Japanese Quail. This study used unsexed Japanese quail chicks, one day old and with an initial weight of 10.3 - 8.8 grams. They were randomly distributed into 4 treatments. Each treatment had three replicates, and each replicate had 15 chicks in cages containing a battery. The current study included an experimental period of (42-72) days for the chicks. The transactions were as follows: T1: Control treatment (without any addition), T2: Treatment of adding Cordyceps militaris 1 mg/kg feed, T3: Treatment of adding Cordyceps militaris 2 mg/kg feed. T4: Treatment of adding Cordyceps militaris 4 mg/kg feed. Blood samples were collected on day 42 of the field experiment to measure cellular blood characteristics represented by (RBC, WBC, Hb, PCV) and some biochemical blood characteristics such as (total protein, glucose, albumin, globulin, cholesterol, triglycerides, creatinine, insulin, Uric acid, liver enzymes ALT and AST, and thyroid hormones T4 and T3. The qualitative characteristics of eggs were also measured. The results of this study showed the following: The highest significant difference (P≤0.05) was obtained for adding the Cordyceps militaris fungus 4 mg/kg feed to the diets on the concentration of red blood cells, white blood cells, blood hemoglobin, and PCV, total protein, albumin, globulin, and triglycerides, creatine, T3, T4. All treatments and the control group did not record any significant difference in the qualitative.