Net profit for July to September stood at 531 billion won ($507 million) compared with 502 billion won a year ago, the company said.
Third-quarter operating profit fell 2.7 percent to 536 billion won due to heavy marketing costs and increased competition.
The company said sales rose 5.9 percent to 4.37 trillion won as its higher-priced 4G long-term evolution (LTE) service attracted new subscribers.
Competition is fierce in the increasingly saturated wireless market in South Korea, which has some 37 million smartphone users in a total population of 50 million.
Wireless operators have tried to boost profits by drawing more customers to faster, higher-priced services.
SK Telecom said 16 million subscribers, or 57 percent of its total clients, now use LTE services.