For further functional development of organic esters of cellulose (CEs), the microcomposition such as grafting or blending with other polymers is a promising approach. Especially, "miscible" polymer blending is practically useful to manipulate the physical properties and functions of CEs readily at the lowest cost possible. N-Vinyl pyrrolidone (VP)-containing vinyl (co)polymers can conditionally form a miscible monophase with CEs; the mixing behavior is seriously affected by the chain length (i.e. carbon number) and DS as to the acyl substituent of the CE component, and also by the VP fraction in the copolymer component. To comprehend the behavior, we measured a viscometric interaction parameter μ and clarified the contribution of attractive or repulsive interactivity between the related polymer ingredients to the miscibility attainment. For the blend system of cellulose acetate/VP-methyl methacrylate copolymer, an additional interest was focused on the molecular orientation and optical anisotropy in drawn films of the miscible blends. The birefringence of the deformed blends was widely controllable, due to cooperative orientation of the two polymer components with a mutually opposite birefringence induced by the drawing process.