This study constructs a dataset of the maturity structure of Japanese government bond for the past half century. Using the maturity composition data at the end of each fiscal year, this study structurally estimates a canonical preferred-habitat term structure model particularly for the subsample period of 1995-2020, during which the short rate fluctuates at low levels. The estimated model with two yield-curve factors well accounts for annual-frequency variations in Japanese bond yields. The study finds that the continued decline in the long-term interest rate in the past quarter century reflects maturity-composition changes.