Built-up area is the result of human activities, which is one of the most important input parameters for the simulation of biogeochemical cycle, and has very important significance for the research of earth system science. Therefore, it is very necessary to map the distribution of built-up area and monitor the changes of it by using new technologies and methods at high spatiotemporal resolution. This article mainly explored the changes of built-up areas at the beginning of the 21st century in Zhejiang Province, China, based on Geographic Information System (GIS) and Remote Sensing (RS). In the article, we first introduced the mapping processes of built-up areas in the study area based on the method which combined object-oriented method and the mapping precision were high. Then, we analyzed the changes of built-up areas in the study area from 2000 to 2005 and 2005 to 2010. Through the study of this article, we got that most of the changes have distributed at the northeast part of Zhejiang from 2000 to 2005, and all parts of Zhejiang except Lishui have significant changes from 2005 to 2010. There were about 1564.07km2 and 1607.73km2 non-built-up areas turned into built-up areas from 2000 to 2005 and 2005 to 2010 respectively. Of course, the contrary conversion also exist which accounted for 22.52km2 and 96.32 km2 respectively. Moreover, the city with the greatest increase of built-up areas from 2000 to 2005 and 2005 to 2010 is Ningbo and Jiaxing respectively.