Real estate market prosperity is crucial to a nation’s economy as well as people’s livelihood, especially for the emerging economy. In China, the real estate market has been overheated since the reform of urban housing system in 1998. Due to the price diversity and region variations, the traditional real estate indicators released by the government became insufficient in explaining local real estate market prosperities. People keep questioning the consistency of the official statistics and the market reality they perceives in their everyday life. This research is an attempt to introduce a sentiment index drawing from Internet data to represent public opinions on real estate market, which reflects the prosperity of real estate market, and contains sentiment information of the society. Methods of data source selection, keywords selection, index construction and index evaluation are proposed and discussed. Empirical results on Beijing real estate market suggest that the proposed index has a strong explanatory power to estimate aggregate real estate indicators, and individual house rent. It is capable to reflect prosperity of the real estate market of Beijing. The index is particular useful to capture public sentiments and expectations on real estate markets and offer insights on future real estate market dynamics.