In most cases, there will be a hard credit pull performed when you apply for a line of credit to determine your credit limit, so just applying can have a short-term negative impact on your credit score.  In addition, line of credit lenders typically report to the three major credit bureaus, which can help to increase your score when payments are made on time. Finally, the amount of your revolving credit line that you use at any given time can have an impact on your credit utilization ratio (similar to the way a credit card would), which does count for 30% of your credit score in the current models used by FICO.