As a general rule, a money order cannot be purchased with a credit card, according to Fox Business News.
The vast majority of vendors of money orders, including check-cashing outlets and the United States Post Office, do not permit money order purchases with credit cards. Some vendors permit the purchase of money orders with a debit card. Occasionally, a local or neighborhood grocery store permits the purchase of a money order with a credit card, but this definitely is a major exception to the rule. Credit card purchases tend to be impermissible because the net effect of such a transaction is taking out a loan to purchase money.