C iprofloxacin (15 mg/kg body weight), amoxycillin (50 mg/kg body weight) and ampicillin (80 mg/kg b. wt.) administered orally to male sharptooth catfish Glorias gariepimts 3 times, every 72 hours intervals. Plasma samples were taken for three successive days after the last dose the most important results were : t) Plasma glucose levels were significantly elevated in fish administered ciprofloxacin and amoxycillin at the 3 days studied and ampicillin at the 3 rd day. In contrast, hypoglycemia observed in the first two days in plasma of C. gariepinus administered ampicillin. 2) Significant hyperproteinaemia was observed in fish groups administered bertfer etpfefkweaein and amoxycillin antibiotics during the three days studied. Ampicillin showed a significant highest value at the second day, while the values at both 1 st and 3 rd days showed significant lower values. 3) Administration of the three antibiotics significantly raised the plasma urea in the three days studied except the 2 nd and 3 rd days in fish administrated amoxycillin and ampicillin respectively. Also, increased plasma concentrations of uric acid and creatinine in C. gariepinus administered the three antibiotics at the three days studied were recorded. 4) The AST and ALT activities in C. gariepinus administered both ciprofloxacin and amoxycillin antibiotics showed significant higher values at the 3 rd day. The slope of rise of AST and ALT activities in both ciprofloxacin and amoxycillin were greater than that of ampicillin that is approximately similar to the control group. So, ciprofloxacin, amoxycillin followed by ampicillin are effective on the liver functions in a decreasing order. This observation is clear in ALT than AST, which indicates that ALT is more sensitive to antibiotic administration. 5) Analysis of ALP activity in all groups of C. gahepinus administered with the three antibiotics in the three periods studied showed significant higher values. The administration of antibiotic may considered as stress factor in the fish even when it used in the prophylactic dose. Glucose and ALT, AST and ALP can used to evaluate the stress condition in fish especially in the farm condition.