In this study, we propose to use an intensity-modulated continuous-wave laser diode-based photoacoustic sensing technique to depict the change in viscosity of a sample. The proposed technique provides the compact, non-invasive, and cost-effective way to determine the change in viscosity. The efficacy of the technique to depict the change in viscosity of the sample is verified through experimentation. Here, five samples having different viscosities are prepared by mixing black ink dye and glycerol in different proportions. Experimentation is performed to obtain the continuous-wave photoacoustic (CW-PA) spectra from each of the samples and subsequently, few frequency domain features are evaluated as the potential marker for determining the change in viscosity of the sample. Also, a novel frequency-domain feature is identified to detect the change in viscosity of the sample. Results reveal that the proposed feature outperformed the conventionally used feature termed as Full Width at Half Maximum (FWHM) as the goodness of fit increases significantly to R2 = 0.98 from R2 = 0.91 (when used with FWHM only).