The war left the Korean peninsula divided and people who lived on the northern side were unable to leave.
The two Koreas, which are technically still at war, have organised reunion events before, but this is the first in three years.
The South Koreans were chosen by lottery - the oldest of them is 101.
A hundred people were chosen by each side to attend the reunion.
Some dropped out after realising the relatives they had hoped to see were no longer alive, so in total there'll be 83 North Koreans and 89 from the South.