Present invention is related to a ventilator adapter and auxiliary chamber thereof. The ventilator adapter of the present invention comprises a T-shaped flow guiding adapter and an auxiliary chamber detachably connected thereto. The T-shaped flow guiding adapter contains a guiding valve that can retractably close or open its opening. The auxiliary chamber is a cylindrical hollow tubing with open ends at both sides, and a chamber partition extended into the interior of the auxiliary chamber, separating the chamber at least partially into two chambers. The present invention is able to be adapted with the conventional ventilator pipeline by using the T-shaped flow guiding adapter for connecting any suitable ventilatory medicine with the auxiliary cavity. When the ventilatory medicine is administrated, the present invention is able to guide the gas flow within the ventilator pipeline reaching into the space of the auxiliary cavity and carrying the ventilatory medicine toward the patient successfully with high amount of medicine doses for better treatment result.