PURPOSE: To prepare backed nonwovens improved in tear strength and dimensional stability and useful as sealing materials for roofing, dam, landfill, or the like.

CONSTITUTION: A treating liquid composition is prepared by adding silica sol to an aqueous solution or suspension of a crosslinkable component-containing copolymer of butyl acrylate and acrylonitrile or a melamine resin and mixing them so that the weight ratio of the copolymer: SiO2 is 3:1-1:3 or the weight ratio of the melamine resin: SiO2 is 10:1-1:1. A spun-bonded nonwoven fabric of polyethylene terephthalate is needle-punched or calendered, which then is soaked in the prepared treating liquid and subjected to liquid-squeezing, drying and heat-treating. Subsequently, the obtained nonwoven fabric is backed with bitumen or PVC plastisol to obtain the objective nonwoven fabric having excellent stretching properties and dimensional stability.