Russia has so far provided South Korea with weapons worth $740 million as a way of repaying some $1.3 billion in debts dating back to the days of the Soviet Union.
Seoul is now in talks on the transfer of cutting-edge technology from Moscow, the South's Defence Acquisition Programme Administration said.
"We have yet to complete negotiations with Russia," a spokesman for the state agency controlled by the defence ministry told AFP, without giving details.
Yonhap news agency quoted a military source as saying the Russian technologies include long-range radar and a defence system against an electromagnetic pulse (EMP) attack.
North Korea is believed to have been developing an EMP system that could disrupt South Korean military communications and radar, it said.
Since the 1950-53 Korean War, South Korea has been heavily dependent on US technology for its arms acquisitions.