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Poly(vinyl alcohol) (PVA) hydrogels were prepared in aqueous solutions at different concentrations using glutaraldehyde (GA) as cross-linker. The gel fraction, increase rate of gels, critical gel point, and swelling ratio were measured. Furthermore, the influences of intramolecular cyclization on the cross-linking processes and the structure of formed hydrogels were studied. The results show that the degree of intramolecular cyclization and the ratio of [−CHO]/[−OH] at critical gel point (rc) increase with the decrease of PVA concentration. The bulk gels do not form when PVA concentration is below 1.1 × 10-2 g/mL even at higher GA/PVA mixture ratio. In the concentration range of (2.20−12.3) × 10-2 g/mL, intramolecular cyclization fraction is basically not changed with gel fraction above the critical gel point. The way of gel growing is controlled by PVA concentration. In a certain range, the lower the PVA concentration is, the higher the increase rate of gels is. The equilibrium swelling ratio decreases w...