The conformation of single poly(methyl methacrylate) chain in the uniaxially stretched film was observed by the combination of the fluorescence labeling technique and scanning near-field optical microscopy (SNOM). The dimension of the individual probe chain (M-w = 1.99 x 10(6)) along the extension axis was evaluated from SNOM image. In the high molecular weight matrix (M-w = 1.89 x 10(6)) the average extension ratio at the single chain level coincided with the macroscopic extension ratio. The distribution of the chain conformation was in good agreement with that of the freely jointed chain followed by affine deformation. On the other hand, the probe chain embedded in the low molecular weight matrix (M-w = 1.76 x 10(5)) showed the smaller extension than that expected from the affine deformation. This suggests that the conformation of the probe chain is affected by the relaxation of the short surrounding chains through disentanglement. (C) 2009 Elsevier Ltd. All rights reserved.