Abstract: UV Spectrophotometry was applied to determination of cinnamaldehyde (CIN),benzaldehyde (BEN) and benzoic acid (BA) in their mixtures.Based on their UV-absorption spectra and by using the iso-absorption point,measurements of absorbance were made at the wavelengths of 228,256,311 nm,and linear relationships between values of absorbance and concentration of the 3 compounds were found as follows:Ccin.=(A311 nm-0.008 4)/0.042 4,Cben.=(A256 nm-0.000 5)/0.062 2-Ccin.,CBA=(A228 nm+0.005 7)/0.061 1-Ccin.-CBA,corresponding to ranges of linearity within 18.03 mg·L-1 for cinnamaldehyde,within 13.08 mg·L-1 for benzaldehyde and within 9.233 mg·L-1 for benzoic acid.Reproducibility of the determination of 3 compounds in a mixture for 6 replicates within a period of 9 h,values of RSD′s found were all less than 1%.Results of tests for recovery obtained for the 3 compounds were in the range of 99.1%-100.5%.