In a recent paper [J Am Ceram Soc. 2018;101:5335-5345], Pakizeh and Moradi studied the structural, morphological, and optical properties of lead zirconate titanate nanopowders. The refractive index and extinction coefficient of samples were calculated based on reflectance and phase angle between the incident and reflected signals for a particular wavenumber. The authors used the Beer-Lamber equation to calculate the reflectance spectra. It is shown in this comment that they have used a wrong relation to calculate the reflectance, and consequently, calculated results based on the reflectance, such as refractive index, extinction coefficient, real and imaginary parts of dielectric constant, LO and TO phonon modes are incorrect.