Today China has the world's largest older population, defined as aged 65 and over. The size of the older population in the United States is also large, ranking third in the world in 2000. The combined older populations of China and the United States represented 29 percent of the world's population 65 and older in 2000. The large older populations in these two countries are projected to more than double in size over the next three decades. Although currently China is younger than the United States and many other countries, its aging process will accelerate in the next few decades, with a speed surpassing the experience of many Western European countries and the United States. This paper examines the current and future situation of the older population in China and compares China's aging with that of the United States, using 2000 and earlier censuses from both countries as well as the population projections data from the U.S. Census Bureau. Growth of the older population, changes in the age distribution in China with comparisons to the United States, and the projections of the older population's future growth are analyzed and presented. The paper also discusses sources of financial support and living arrangements in China and the United States. Finally, the paper assesses trends in the older population support ratio and the implications for the economic well-being of an aging population.