This study examined the effects of acid treatments on the length of multiwalled carbon nanotubes (MWCNTs) as well as the influence of the aspect ratio of the MWCNTs on the electrical percolation threshold. In particular, the length distribution, intensity ratio of the G and D Raman peaks, BET surface area, and maximum decomposition temperatures of the MWCNTs were investigated. The MWCNTs showed different electrical percolation thresholds depending on the aspect ratio. The higher aspect ratio MWCNTs had lower electrical percolation thresholds than those with smaller ratios due to their ease of contact with other MWCNTs. In terms of the electrical behavior of a MWCNT film, many more short MWCNTs were necessary to reach the electrical percolation threshold than long MWCNTs. These results demonstrate the need to control the aspect ratio of MWCNTs in order for them to be used efficiently in electrical applications. (C) 2009 Elsevier B.V. All rights reserved.