The present study was conducted to investigate the pharmacokinetics of tilmicosin (25 mg/kg b.wt.) following single and repeated oral administration (once daily for three consecutive days) as well as tissue residues in normal and experimentally Mycoplasma gallisepticum-infected broiler chickens. Following single administration of tilmicosin in normal chickens, the drug reached its maximum serum concentrations (Cmax) after 2.45±0.01 h of administration with value of 0.97±0.04 µg/ml. Absorption half-life (t0.5ab) of tilmicosin was 0.89±0.02 h and the elimination half-life (t0.5el) was 14.73 ±1.24 h. The repeated oral administration of tilmicosin in normal and Mycoplasma gallisepticum- infected chickens revealed a lower significant serum tilmicosin concentration after all times of sampling in infected chickens compared to those of normal chickens. Tilmicosin residues was assayed in lung, kidney, liver, heart, breast muscle, thigh muscle, fat and skin after 24, 48, 72, 96, 120 and 144 h post last dose. The results showed that the highest residue values were recorded in lung followed by liver and kidneys while the lowest values were recorded in heart. Tilmicosin residues were not detected in all tested tissues except in lung till 5th day after sessation of drug administration. However, all the tested tissues were free from tilmicosin residues after 5th day after sessation of tilmicosin administration and this suggest a withdrawal period of five days for tilmicosin in broiler chickens. In conclusion, timicosin has rapid absorption, long elimination half-life, rapid and extensive penetration from blood into tissues especially lungs. Additionally, timicosin had a short