Poly(N-vinylpyrrolidone) (PVP) is miscible with cellulose acetate (CA) with a degree of acetyl substitution (DS) of less than ca. 2.75, and a random copolymer of N-vinylpyrrolidone (VP) and methyl methacrylate (MMA) can also form completely miscible blends with CA, when the VP fraction in the copolymer is > 30 mol % and the DS of CA is <= 2.5. The molecular orientation and optical anisotropy induced by uniaxial deformation of the miscible blends of the VP-containing vinyl polymers [P(VP-co-MMA)s] with CA were characterized by a fluorescence polarization method and birefringence quantification, respectively. Film samples of more than 10 pairs of CA/P(VP-co-MMA) were cast from mixed polymer solutions in N,N-dimethylformamide containing a slight amount of a stilbene derivative as a fluorescent probe, to assume different blend compositions for each individual polymer pair. Through analysis of polarized fluorescence intensity, it was found that all the drawn films gave a positive orientation function, but the orientation development became suppressed with increasing content of the vinyl polymer component. In comparison between different CA/PVP series, the drawn blends comprising a CA of comparatively lower DS and a PVP of higher molecular weight indicated a higher degree of orientation at any stage of elongation. The molecular orientation in CA/VP-MMA copolymer blends was affected by the DS of CA in a similar manner to that in the CA/PVP series, but the VP:MMA ratio in the copolymer was less effective. The optical birefringence of the drawn films, when compared at a given draw ratio for a series of blends, decreased drastically with an increase in the vinyl polymer content and changed from positive to negative values at a certain blend composition. This optical behavior is interpretable in terms of an effect of birefringence compensation due to the positive and negative contributions of oriented CA and vinyl polymer, respectively, to the overall birefringence. The critical binary composition where the blend remains a birefringence-free material shifted to the CA-rich composition side with increasing DS of the CA used as well as with increasing VP fraction in the P(VP-co-MMA) component. At vinyl polymer-rich compositions, the negative birefringence observed for the drawn blends was even greater in absolute value than that of the drawn, unblended vinyl polymer, suggesting that the two constituent polymers can orient cooperatively as a result of their high miscibility.