Balance transfers have a minimal impact on your credit score. It's what happens before and after the transfer that can affect your credit score. If you open a new credit card account to transfer your balance to, you will have what's known as a "hard inquiry" on your credit report. This can cause your score to drop by a few points because it's an indication that you're looking to acquire more credit.
The point of a balance transfer is to pay less interest so you can pay off your balance sooner. If you do this, preferably before the introductory balance transfer rate expires, your credit score will improve over the long term.