Although phthalate esters contribute to airway remodeling by increasing bronchial cells’ migration and proliferation, the relationship between human exposure to phthalates and asthma is not understood. We measured phthalate exposure in the human body and evaluated its effect on asthma. Asthma (n= 123) and asthma-free (n= 139) participants were, respectively, recruited from an asthma clinic and the community in Taiwan. The urine levels of six phthalate metabolites were determined by liquid chromatography tandem mass spectrometry. Compared with the controls, male asthma patients had higher means of mono-(2-ethylhexyl) phthalate (MEHP) (116.3 nmol/g), monobutyl phthalate (MBP) (850.3 nmol/g) and monoethyl phthalate (MEP) (965.8 nmol/g), and female patients had greater MBP (2902.4 nmol/g). Each 10-fold increase in the level of these phthalate metabolites was correspondingly associated with a 5.0-, 5.8-, 4.2- and 5.3-fold risk of contracting asthma. Male asthma patients were identified to have a higher proportion of MEHP exposure (32.5%) than the controls (25.3%). In asthma patients, an increase in urine MEHP levels and the total phthalate metabolite concentration were notably linked to increased risks of emergency room visits and being hospitalized. For the occurrence and acute clinical events of adult asthma, phthalate exposures and MEHP retention may contribute to higher risks of contracting this respiratory disorder.