In acetone solution, uniform polyaniline (PANI) nanospheres have been successfully synthesized by using cellulose acetate (CA) as a single template, which provides the first example of uniform PANI nanospheres synthesized in nonaqueous system. Our result exhibits that the CA micelle in nonaqueous medium plays a unique role in controlling size and uniformity of PANI nanospheres. A detail formation mechanism for the uniform PANI nanospheres has been proposed. In addition, the gas sensitivity and time response of the PANI nanospheres to NH3 gas have been investigated, which shows superior gas sensing performance even at 1 ppm of NH3 gas. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012