The rheological and rheo-optical properties of solutions of high molecular weight polyvinylalcohol (PVA) with different syndiotactic diad contents in dimethylsulfoxide (DMSO) were investigated in terms of tacticity, molecular weight, and degree of saponification. Tacticity played a significant role in rheological behavior. Over the frequency range of 10(-1) to 10(2) rad/s PVA with syndiotactic diad content of similar to 53% (atactic PVA) exhibited almost Newtonian flow behavior whereas PVA with syndiotactic diad content of similar to 63% (syndiotactic PVA) exhibited Bingham flow behavior. On the plot of storage modulus (G’) against loss modulus (G ") atactic PVA gave slopes of similar to 2 while syndiotactic PVA gave slopes of similar to 1. With syndiotactic PVA, an increase of shear rate notably increased flow birefringence (Delta n(f)) at shear rates higher than 5 sec(-1). On the other hand, only a slight increase in Delta n(f) was observed in the case of atactic PVA. The effects of molecular weight and degree of saponification were discussed as well.