The prevalence of asthma keeps on increasing worldwide, especially in western societies over last 40 years. The mechanism of asthma is unclear. Recently, concern about indoor air pollution as a risk factor for asthma has been arisen. In present study, 25 Kun Ming male mice were placed in an air chamber containing respective formaldehyde (FA) concentration of 0, 0.5, 1.0, 3.0 mg/m3,and 3.0 mg/m3 with Capsazepine (CPZ, a specific antagonist of vanilloid receptor)-pretreatment in five testing groups (n=5 per group) for inhale experiments. The inhaled groups were exposed to gaseous FA for 6 hours each day in 10 successive days. After exposure, the concentrations of IL4 in blood serum and broncho alveolar lavage fluid (BALF) were measured. Experimental results showed that the IL4 level in serum was too low to be detected; and the concentrations of IL4 in BALF increased in a dose-dependent manner. However, for the CPZ-pretreated group the IL4 level in BALF decreased significantly (compared with 3.0 mg/m3 FA inhaled group, p<0.01). This paper describes experimental animal methods to probe IL4 level, an important indicator for IgE response. The studies in this paper indicated that gaseous FA might induce acquired atopy by type II VR1 signaling system. These findings suggested that indoor air pollutants such as FA might be key risk factors for the rise in asthma cases, and type II VR1 signaling system might be one of the mechanisms for the rise.