To detect changes in DNA and/or protein structures of phage T7 under different ionic strength, Raman spectra of phage T7 have been recorded in solutions of three different NaCl + Tris concentrations. Iterative Jansson-Van Cittert deconvolution, as well as decomposition methods have been used to quantify changes in DNA structure. Significant modifications in ratios of contributions from 675 and 685 cm−1 vibrations, as well as in the DNA backbone vibrations, characteristic for B-DNA, near 835 cm−1 frequency have been found. Changes of the base electronic structure were identified in the interval between 1280 and 1400 cm−1. Estimation of the overall protein structure suggests predominant β-sheet content.