The molecular shape of well-defined poly(2-ethyl-2-oxazoline) (PEOz) chains in tetrahydrofuran (THF at room temperature has been studied by a combination of static and dynamic light scattering and viscometry in the framework of the hard-sphere model. Data of the z-average radius of gyration as well as equivalent sphere radii such as the hydrodynamic radius (R-H), the viscometric radius (R-v), and the thermodynamic radius (R-r) give some evidences of sphere-like structure. The unperturbed molecular dimension (((R-G(2)> (0)/M-w)(infinity)(1/2) = 624 x 10(-4) nm) determined by an indirect method and the persistence length q = 0.70 nm determined by the Bushin-Bohdanecky method appear to be quite small compared to those of common flexible polymers. In particular, the R value (24.0), defined by (1/2)/q, being of a considerably higher order than unity allows an estimation that the chain possibly has a type of "random Gaussian globule". Based upon the experimental results so far obtained, it can be concluded that the chains of PEOz in THF at 25 degreesC assume basically a shape that is very similar to that of a sphere in the least draining limit. Both the branch-like structure of the PEOz molecule and the intramolecular polar interaction between the nitrogen of the main chain and the carbonyl carbon in the side group are considered to be responsible for the chain contraction.