A senior member of the ruling Liberal Democratic Party said Miyazawa wasn't suffering from any specific illness when he died, Kyodo News reported Thursday.
Miyazawa, who served as finance minister before he was elected prime minister, helped to guide the Japanese economy with policies of aggressive budget expansion through the 1980s and 1990s.
Miyazawa participated in a 1951 trip to San Francisco by Prime Minister Shigeru Yoshida to sign a peace treaty that resolved many issues stemming from World War II. In 1953 he won his first parliament seat as a member of the House of Councilors. He served a total 14 terms in both houses of parliament before retiring in 2003, Kyodo said.
During his tenure as prime minister, Miyazawa passed a law allowing for the Japanese Self-Defense Forces to be dispatched overseas for U.N. peacekeeping operations.