The present study elucidates the effects of solvent quality and polymer concentration on the aggregation behavior of polyvinyl alcohol (PVA) solutions from the dilute solution to semi-dilute solution regions. Combination of the results in static and dynamic light scattering indicates that in dilute solution the thermodynamic driving forces primarily dominate the dynamic behavior of PVA/N-methylpyrrolidone (PVA/NMP) solution. In contrast with PVA/water solution, the hydrodynamic interaction would dominate the dynamic behavior of the solution. The concentration dependence on the dynamic behavior of semi-dilute solution has also been studied through DLS measurement. For PVA/water solutions, the hydrodynamic correlation length of fast mode has a concentration dependence given by xi (D), = [eta ]C-0.42, and the value of exponent is close to the predicted value from scaling theory in the marginal solvent. On the other hand, for PVA/NMP solutions the value of exponent is close to the predicted value from the scaling theory in good solvent limit: -0.75. However, contrary to the expectation, the gelation behavior could not occur in PVA/water solutions at the same condition of gelation in PVA/NMP solution even though the affinity of water to PVA is much lower than that of NMP. In this work, we considered that the PVA/NMP solution might possess a character that could form a homogeneous network structure. The intermolecular associations must play a dominant role as soon as the chains start to overlap in PVA/NMP solution. On the other hand, combining the DLS result with our previous work, the gelation of PVA/NMP solutions is considered due to complex formation in the transient network junctions, i.e. the formation of molecular complex is crucial to the physical gelation in a good solvent system.