The woman, whose name is not known, has been seen accompanying Kim at several public appearances.
"From the protocol point of view, such as this woman's place and table settings, it is highly likely that she's his wife and first Chairman Kim must actually be married," the government source told Yonhap.
Few personal details are known about Kim, such as his age or if he is married.
"Everything related to Kim Jong Il's children is a deadly secret. No sane North Korean who knows it would share this out for very special reasons," said Andrei Lankov of Kookmin University in South Korea, an expert and author of several books on North Korea.
The presence of a wife accompanying Kim to an official engagement could be an attempt to dispel misgivings among North Koreans that their leader is too young, Yonhap reported Saturday.