The effect of several new binary accelerator systems were studied with special emphasis to the relationship of nucleophilicity to their rheological and mechanical properties. In this study, dialkyl/azacycloalkyl substituted benzoylthioureas (BTU 1-5) were used as secondary accelerators (SA) along with three different primary accelerators (PA) viz., Cyclohexylbenzthiazylsulfonamide (CBS), Mercaptobenzothiazole (MBT) or Zincdithiocarbamate(ZDC) in the sulfur vulcanization of natural rubber. The effect of these secondary accelerators on the rheological and mechanical properties was found to be improved when compared to the reference mixes. It is noted that the N-benzoyl-N'N'-piperidinylthiourea (BTU 4) is more effective as a secondary accelerator due to the higher nucleophilicity of the same when compared with the test compounds. The ZDC-BTU gives the best result as binary accelerator system in natural rubber. Chemical characterization was carried out by determining the total crosslink density. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012