Keeping in view the significant facts on Zinc Oxide (ZnO) and Poly (Vinyl Alcohol) (PVA), we developed nanocomposite films comprising small weight percentage of ZnO content in host polymer PVA, choosing a simple and cost-effective method based on solution-casting. The investigations of its structure, microstructure, linear/luminescence and nonlinear optical properties are presented. This article mainly discusses the intense low threshold nonlinear absorption (NLA) behaviour displayed by the samples, as studied using the standard Z-scan technique. On either increasing the intensity or ZnO content, the samples exhibited a switchover from saturable to reverse saturable absorption, which is rarely observed under 442 nm continuous wave (CW) laser light excitation. The effective values of nonlinear absorption coefficient and imaginary part of third-order nonlinear susceptibility are higher than the recently reported results. The limiting threshold values (obtained from optical limiting curves) are also found to be much better than other reported ones.