The aim of this work is to evaluate the effect of aging conditions catalysts based on neodymium salt on polymerization conversion, catalyst activity, and polymer characteristics. The synthesized catalysts were aged at 1.0, 25, 40, and 60 degrees C for 24 and 48 h. The polybutadienes were characterized by size exclusion chromatography to determine the molecular weight characteristics and infrared spectroscopy to determine the microstructure. The results showed that the stereoselectivity of active catalyst sites was not affected by the aging conditions. However, the molecular weight increased with aging temperature. The catalysts aged at 25 degrees C showed a trend to attain higher activities than those aged at 40 and 60 degrees C. Moreover, a significant drop on polymerization reaction rate occurred as the catalyst aging temperature increased. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1496-1502, 2009