The present study employed the College Entrance Examination Center (CEEC) Interest Inventory to examine the structure of vocational interests among high school students in Taiwan. Holland´s simple circular and calculus hypotheses as well as Gati’s hierarchical model and two-group partition model were tested. Data from 10,626 Taiwanese high school students were randomly divided into two samples, (Sample A and Sample B). Factor analysis on sample A revealed a six-factor structure consistent with the RIASEC types. Sample B was used to vigorously test Holland’s hypotheses and Gati’s models. Holland’s  simple circular hypothesis and the calculus hypothesis were supported by multidimensional scaling and randomization test, respectively. Gati’s hierarchical model was supported by factor analysis and hierarchical clustering on six interest type scores. Also, Gait’s three-group partition model (RI, AS, EC) as well as a two-group partition model (RI, ASEC) were found by factor analysis, multidimensional scaling, hierarchical clustering, and randomization test. Research findings reported by Ou (2011) were used to examine the practical usefulness of the partition models. It was suggested that the two-group partition model might be more useful for career counseling among high school students in Taiwan than the three-group partition model. A survey suggested that the structure of the vocational interests perceived by high school counselors were similar to those found in the analyses, supporting Holland’s hypotheses and Gati’s models.