The deformation associated with the photocuring reaction of an anthracene-labeled polystyrene (PSA) in a miscible blend with poly(vinyl methyl ether)(PVME) was in situ monitored at ambient temperature by using Mach-Zehnder interferometry (MZI). The curing kinetics of a PSA/PVME (30/70) blend was followed by observing the decrease in the absorption of the anthracene moieties upon irradiation using UV-visible spectroscopy. It was found that both the kinetics of the curing and deformation processes can be well described by the modified Kohlrausch-Williams-Watts (KWW) empirical function. The experimental results reveal a strong correlation between the photocuring and deformation processes of the blend. From the dynamic mechanical measurements performed for samples with different irradiation times, it was also found that the deformation process of the blend observed by MZI is controlled by the on-going cross-link-induced glassification process of the mixtures. These experimental results suggest that MZI is a useful technique to monitor in situ the local deformation and relaxation processes in photoreactive polymers. (C) 2010 Elsevier Ltd. All rights reserved.