The subgrid scale (SGS) variance for a high‐Schmidt‐number passive scalar of Sc >> 1 is measured using a high‐resolution planar laser‐induced fluorescence technique in a grid‐generated turbulent liquid flow, and the values of the model coefficients in the scale‐similarity model and the scalar‐gradient model used for estimating the SGS scalar variance are experimentally evaluated. The results show that for both models, the measured values are much larger than the well‐known values obtained in the previous studies done for non‐high‐Sc scalars of Sc ≅ 1. Similarly, the measured value of the model coefficient in the scalar‐gradient model tends to be larger than the value estimated by the dynamic procedure. The increases in the measured values of the model coefficients for the high‐Sc scalar can be explained by the presence of the viscous‐convective range showing a nearly (−1)‐slope in the high‐wavenumber range of the power spectrum of concentration fluctuation. © 2011 American Institute of Chemical Engineers AIChE J, 2012