We report the experimental observation of intermittency in a partially-coherent optical wave system accurately ruled by the one-dimensional defocusing and integrable nonlinear Schrodinger equation (1D-NLSE). Using fast detection techniques, we observe that the probability density function of light fluctuations is characterized by tails that are lower than those predicted by a Gaussian distribution. Moreover, by applying a band-pass frequency optical filter, we reveal the phenomenon of intermittency, i.e. small scales are characterized by large heavy-tailed deviations from Gaussian statistics, while the large ones are almost Gaussian. These phenomena are very well described by numerical simulations of the 1D-NLSE. In particular, the one-mode probability density function for an individual Fourier mode shows tails having a weight that increases with the mode frequencies.