This study was conducted to develop the Chinese Mandarin State-Trait Anxiety Inventory Y form and to evaluate its psychometric properties among Taiwanese outpatients with anxiety disorders. A three-phase survey questionnaire was used to gather cross-sectional data. Non-hospitalized adults (n= 306) with anxiety disorders were recruited from mental health clinics in central Taiwan. Cronbach's alpha reliabilities for the state and trait anxiety subscales were 0.91 and 0.92, respectively. The 2-week test-retest reliabilities for the state and trait anxiety subscales were 0.76 and 0.91, respectively. Criterion validity of the scale was supported by its high correlations with the interview version of the Chinese Hamilton Anxiety Rating Scale (r= 0.69 for state and 0.74 for trait anxiety). Construct validity of the scale was confirmed by a four-factor structure, showing slightly adequate representation of the data. The scale was shown to be reliable and may be valid for measuring anxiety in Taiwanese adults with anxiety disorders.