The Thai Airways pet policy is as follows:
Pets are not accepted in the aircraft cabin, but are accepted as checked baggage.
Pets are not allowed on the following routes due to quarantine or other conditions: flight to Auckland, Denpasar, Dubai, Hong Kong and London; flight to/from Brisbane, Melbourne, Perth and Sydney; and flights operated on aircraft A320.
Thai Airways bans certain dog breeds from acceptance as checked baggage. (For cargo acceptance, please contact directly to Cargo Department).
Thai Airways also accepts unaccompanied pets as cargo; this service allows passengers to transport other pets, not only dogs and cats.
Taking a pet to a foreign country involves preparation and planning far in advance of your departure date. Requirements for pet travel to a foreign country are set by the destination country. If you are you traveling to another country and bringing along your pet you’ll need to meet the animal health requirements of the country you are visiting.
More information on the Thai Airways pet policy