The Nikkei 225 peaked in December 1989 before Japan’s asset-price bubble burst.
The index reached an intraday record of 38,957.44 on December 29, 1989. It then fell sharply during the early 1990s as Japan’s inflated property and equity markets deflated. The episode is commonly known as the bursting of Japan’s asset-price bubble.
Easy credit, rising land prices, speculative investment, and optimistic expectations had pushed asset values to extraordinary levels during the 1980s. When monetary policy tightened and confidence changed, both stock and real-estate prices declined. The resulting economic stagnation became associated with Japan’s “Lost Decades.”
The Nikkei 225 is Japan’s best-known stock index, but TOPIX is another major Japanese benchmark. The question’s answer is specifically the Nikkei 225 because its December 1989 record became the emblematic peak of the bubble.