Bangkok to Beijing and then return to Bangkok, 72 hour exemption applicable?

Hi Jen, I'm afraid the 72 hour free transt is not applicable to your situation. To enjoy the policy, you have to go onto another country or region other than Thailand and mainland China. I suggest you fly from Beijing to Hong kong or Macau and then fly from there to Bangkok, as both Hong Kong and Macau grant a 30-day free pass for Thailand passport holders.