Assuming that you are bringing your pet(s) into Thailand for 6 months or more by air as one of accompanied baggage:

Authorization to import your pet arriving by air can be obtained at the Bangkok airport.
At the airport, you will need to obtain an authorization to bring into, or transit animals via Thailand (Ror 6 form), and a permission to bring animals into Thailand (Ror 7 form). Fill out the application for special importation form (Kor Sor Kor 102). Please be advised that you may be required to pay fees on the above applications and import duties on your pet. Import duties will be exempted if your pet will be in Thailand for 6 months or less. However, you will need to fill out a guarantee form and pay a deposit at the airport.
Other requirements:

Identity certificate signed in country of origin by a registered veterinarian, describing age, breed, sex, color, etc.

Rabies vaccination certificate, your pet must be vaccinated at least 15 days prior to departure.

Leptospirosis vaccination certificate, at least 21 days prior to departure Animal must be healthy and free from any sign of infectious or contagious disease

Animal had been resident in Canada not less than 6 months before date of departure. If you have further questions please contact:

Bangkok Airport Customs Office

Web:http://www.customs.go.th/
Tel. (66-2) 535-1269, 535-1153, 535-1680, 535-6463

Department of Livestock Development, Bangkok

Tel: 66 2 252-6944
Fax: 66 2 251-8206
URL: www.dld.go.th
E-mail: info@dld.go.th