Breast cancer is one of the leading causes of death among women in Japan. Its mortality rate has been increased in recent years. However, there has been no study examining the changes in premature mortality in Japanese women. In the present study, using two health indicators, years of life lost (YLL) and average of years of life lost (AYLL), we estimated the premature mortality due to breast cancer in Japan during the period from 1995 to 2006. YLL indicates how many years that life of a patient was shortened with the presence of cancer, and AYLL provides an average loss of expected years of life among these deceased persons. Results showed an increase in total YLL due to this condition from 204,840.6 years in 1995 to 255,046.9 years in 2006. In each calendar year, YLL remained the highest in the group aged 50-59 years, accounting for 32%-36% of annual YLL. In contrast, we found a decrease in AYLL of breast cancer from 26.4 years in 1995 to 22.8 years in 2006; namely, breast cancer patients who died in 2006 lived an average 3.6 years longer than those who died in 1995. In conclusion, we show the decrease in AYLL of breast cancer deaths, despite the increase in total numbers of annual YLL during the study period. Thus, women with breast cancer have benefited from postponement of the deaths in 2006, compared to those in 1995, which may be related to the improvements in medical health care or appropriate prevention.