Background: Drug information service is an essential supportive service to the health care practice. Quality assurance is an ongoing process to improve and maintain quality of drug information services. In this study we focused of assessing the protocol adherence for drug information services. Methods: The study was conducted for the drug information services in a rural South Indian hospital for a period of two years (2011-2012). Assessment was done on adherence to the protocol and satisfaction of customers. Results: A total of 726 queries were answered in the study period which include 335 in 2011 and 391 in 2012. Average number of queries answered per month in 2011 was 28 (SD ± 20.6) and in 2012 was 33 (SD ± 24.8). Consistency of the service was poor the number of queries answered per month range between zero to 92. Most of the May month is a vacation time and the center was not working. Protocol adherence increased in the study period. The highest level of adherence was seen in the months of April, August, October, and November in the year 2012. Customer satisfaction could be achieved above 85% in the months of April, August, September, October, and December of 2012. Conclusion: The protocol adherence in the study center for drug information increased in the study period and thus was the customer satisfaction. Future studies could assess other measures of quality assurance of drug information services.