There are two different payment addresses for Sallie Mae. If you are a direct borrower, the address is: P.O. Box 8459, Philadelphia, PA 19101-8459. If you are a co-signer of a loan, the address is: P.O. Box 8377, Philadelphia, PA 19101-377.
There are other ways to send a loan payment to Sallie Mae. If you have an account set up online, you can pay directly online. Also, you can set up recurring payments through your bank. You can make payments over the phone by calling 800-472-5543. No matter how you make your loan make sure you have your account number and, if possible, your remittance slip.