Biaxially oriented polypropylene (BOPP) film accounts for a large amount of polypropylene since it is well suited for food packaging films or industrial films, because of its high performance in terms of mechanical and optical properties. Recently machine speed has been increasing to obtain higher production rate and film thickness has become thinner to reduce the environmental load. To meet the demands, many researchers have been investigating stretchability of PP by connecting the stretching force at the yield point and crystalline structure. Many other studies have been conducted regarding the surface structure of BOPP. Although there were some cases that crater-like film surface roughness was formed on BOPP films, the formation mechanism of craters has not been clarified. In this report, new hypothesis of the crater-like film surface roughness formation mechanism is proposed by observing the transformation of crater from sheet to BOPP film and by investigating the relationship between the stressstrain curve and surface roughness change. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012