In the procedure of the life cycle assessment complying with ISO 14000 series, impact assessment is required. For the integrated assessment of impacts, evaluation with economical values is frequently applied. Evaluating impacts of damages on human health, it is converted to economical value using method of environmental economics. One of the ways to determine the rates of conversion is to presume residents' willingness to pay to avoid the damages. These rates are estimated by analyzing data observed through social survey, but knowledge of the conversion rates in developing countries is not sufficient. We launched a social survey in Shanghai to analyze willingness to pay to decrease risks contracting asthma caused by air pollution. Five hundred subjects were sampled by multistage area sampling. Subjects were sampled from all of the districts of Shanghai. They were asked their willingness to purchase an air purifier to reduce risks to contact asthma with presented prices for the analysis of contingent valuation method, as well as their profiles. The answers were analyzed by fitting log-logistic distributions and factors that influence the willingness were examined.