In this work, the effect of two antifouling materials on the activity of catalyst used to produce polyethylene in a 1-L slurry reactor and on the titanium oxidation state of the catalyst was investigated. Armostat 300 with the formula alkyl C-14-C-18 bis(2-hydroxyethyl)amine is an antistatic agent that reduces static electricity of the polymer particles. It was found that within the concentration of 0.16-1.32 g/mmol Ti, Armostat 300 helps to increase the catalyst activity to 1.3-2 times. The variation of the titanium oxidation state of the catalyst in the presence of Armostat 300 at 80 degrees C with Al/Ti molar ratio of 100 showed that Ti (III) species increased. The effect of Armostat 300 on T-m, % X-c, density, bulk density, and MFI of polymer was insignificant. In this work, Zonyl FSN-100 with the formula R-f(CH2CH2O)(x)H, R-f = F(CF2CF2)(y), Y = 1-9, x = 1-26 was used as antifouling agent in copolymerization of ethylene with 1-butene. It was found that Zonyl FSN-100 at the concentration range of 5-20 ppm reduces the catalyst activity to 1.11-1.9 times. It was also shown that Ti (III) species in the presence of Zonyl FSN 100 decreased. This antifouling agent slightly decreased the properties of polymer including % X-c, density, and M-w. (c) 2006 Wiley Periodicals, Inc.