Per rule of law, imposition, reduction or exemption of tax shall be regulated by law. Therefore, imported goods which are exempt from Customs duty shall be stipulated in Customs Act, the Customs Import Tariff, or other laws.

1. Stipulated in Customs Import Tariff:
   1. The tariff rate listed in the "Rate Column" is zero.
   2. For items subject to conditional duty imposition, reduction or exemption, the qualifying conditions are specifically laid down in the "Additional Notes" in the chapters concerned.
2. According to Duty Exemption Section in Chapter III of Customs Act:
   1. Exempt of duties according to international general rules
   2. Lost or damaged goods
   3. Compensation or replacement goods
   4. Goods temporarily imported or exported 
   5. Re-exports of raw materials imported for manufacturing articles
   6. Re-imports of exported products returned from abroad

   Imported goods exempt from customs duty under Article 49 of the Customs Act shall be verified by Customs against the tax-exempt regulations, special terms and conditions or evidential documents issued by competent agencies. 

3. According to other laws, such as Atomic Energy Law, which states that duties for equipment imported for nuclear research use may be reduced or exempted.