Log in to Citibank Online (r) at www.citibank.com.vn with your user ID and password. Select "Services/My profile". Click "Card activation" and select your card name for activation. www.citibank.com.vn > English > Online Services > Card Activation Guide to Activate Your Credit, Debit, or ATM Card Online - Citibank www.citibank.com.vn > English > Online Services > Card Activation