To identify Hf species and quantitatively evaluate their acid properties, combined measurement of infrared (IR) and temperature-programmed desorption (TPD) with deuterated acetonitrile (CD3CN) as probe molecule was performed on Hf-Beta and HfO2/Si-Beta. IR spectra of CD3CN adsorbed on Hf-Beta showed five types of Hf species including framework open and closed Hf sites, extra-framework HfO2, and two types of Hf species bearing hydroxy groups. IR measurement showed structural change in Hf-Beta upon exposing to water vapor with generation of the two types of Hf species bearing hydroxy groups. Integrated molar extinction coefficients for C N stretching vibration of CD3CN adsorbed on these Hf species were estimated and the number of each Hf acid site was calculated. Acid strength of these Hf species was estimated from CD3CN-TPD measurement in combination with IR; the acid strength of the open and closed Hf sites, extra-framework HfO2 species, and the other Hf species was found to be strong, moderate, and weak, respectively.