Plastics films have been widely used in food packaging. But due to the environmental concerns of plastics films, there is a trend of replacing plastics films with paper for food packaging. To meet the requirements of packaging, the paper must be modified to improve its barrier properties. In this report, a sonication and dip coating method was developed to deposit a PVA/MMT nanocoating on two representative paper substrates: regular paper and cotton paper. The coated paper substrates were characterized by X-ray diffraction, scanning electron microscopy (SEM), water vapor transmission rate (WVTR), and microscale combustion calorimetry (MCC). The XRD results support the formation of well-aligned MMT nanosheets on paper substrates and the SEM images show that most pores on the substrates were covered by the nanocoatings, which leads to a drastic decrease in WVTR of the coated substrates. The nanocoatings also led to a minor improvement in flame retardancy. The results suggest that applying nanocoating is a promising approach to improve the barrier properties of paper for potential packaging applications.