NiO with multilayer structure was prepared by impregnating electrospun polylactic acid (PLA) nanofibrous webs with nickel acetate solution and subsequent calcination. From SEM images, it can be observed that the structures of NiO products from surface to center were nanogrooves inlaid film, hollow pores and honeycomb-like nanofibers with nanogrooves, successively. The formation mechanisms were studied in detail by TGA and DSC. FT-IR and XRD measurements demonstrated that the product was highly pure NiO with cubic structure. The sensitivity of the NiO products to formaldehyde was investigated. As a result, the multilayer NiO exhibited much higher sensing signal than NiO powders. This indicated that the prepared multilayer NiO could be used as a candidate to fabricate formaldehyde sensors. (C) 2013 Elsevier B. V. All rights reserved.