The Japanese stock index that peaked on 29 December 1989 was the Nikkei 225.
The Nikkei 225 reached an all-time closing high of 38,915.87 on December 29, 1989. Its peak marked the end of Japan’s extraordinary late-1980s asset-price boom, during which property and equity values rose to levels later considered unsustainable.
After the peak, Japanese shares fell dramatically as the bubble deflated. The decline was accompanied by banking problems, falling land prices, weak growth, and prolonged deflationary pressure. Japan’s extended period of economic stagnation is often called the Lost Decades.
The Nikkei 225 is a price-weighted index of 225 major companies listed on the Tokyo Stock Exchange’s Prime Market. It is not identical to TOPIX, which uses a different methodology and broader coverage. That distinction matters when comparing historical Japanese market records.