The meetings will take place in October at a mountain resort in North Korea.
The decision follows an agreement last month that de-escalated tensions sparked by a border mine explosion that injured two South Korean soldiers.
Thousands of Korean families have been separated with little or no contact since the war ended in 1953.
The highly emotional reunions of family member who have not seen one another in decades have been infrequent, and depend hugely on the state of relations on the peninsula.
The BBC's Stephen Evans in Seoul says the reunions, which started in 1988, used to be annual but have often been cancelled in recent years as relations frayed. The last round was held in February 2014.
About 66,000 South Koreans remain on the waiting list to see their relatives, many in their 80s and 90s, our correspondent adds.
The upcoming reunions, slated to be held at the Diamond Mountain resort in Mount Kumgang from 20 to 26 October, will see 100 people from each side selected.
Source: Korea Red Cross
The decision came after Red Cross officials from both countries held talks earlier this week at the border village of Panmunjom.
Communication between relatives across the border is highly restricted and almost non-existent. The two countries remain technically at war as the Korean War ended with an armistice.
North and South Korea have agreed to hold rare reunions for families separated by the Korean War, according to Seoul.