Lignin nanospheres/poly(vinyl alcohol) (LNS/PVA) nanocomposite films were prepared through solvent casting approach. Compared with lignin/PVA blend film, LNS could be evenly dispersed in PVA matrix, and the nanocomposite films did not generate macroscopic phase separation. Maximum decomposition temperature (T-max) and glass transition temperature (T-g) of pure PVA film were 264.7 and 104.2 degrees C, while the T-max and T-g of the nanocomposite film containing 1 wt % LNS increased to 272.1 and 116.8 degrees C, respectively. Moreover, with increasing of LNS content in PVA matrix, the T-max and T-g of the nanocomposite films gradually increased. Adding a certain amount of LNS in PVA could improve mechanical strength of the films under the condition of elongation at break in a small amount of loss. The nanocomposite films outperformed the lignin/PVA blend film in UV-absorbing and transparency, which are a promising candidate for medicine bottles and food packaging.