Am I legally liable for accidentally using a found credit card for a small purchase?

According to Article 196 of the Criminal Law of the People's Republic of China, using a credit card without the owner's permission (including found cards) constitutes credit card fraud. The liability depends on the amount: if it reaches 5,000 yuan or more, you may face criminal charges with imprisonment up to five years or detention, plus fines. Even below this threshold, it could violate the Public Security Administration Punishments Law, leading to up to 15 days of detention and 1,000 yuan in fines.

In your case, though the amount is small and the use was accidental, unauthorized use without the owner's explicit consent is still a violation. To mitigate risks, immediately report to the police, explain the situation truthfully, contact the card-issuing bank to notify the unauthorized transaction, and return the 20-yuan amount to the owner or bank as soon as possible. These proactive actions can help reduce potential legal consequences.