Ultraviolet (UV) stability of gamma-irradiated poly(tetrafluoroethylene), 2 degrees-PTFE, powder-filled low-density polyethylene (LDPE) was studied in this work. The mechanical and thermal properties of 2 degrees-PTFE powder-filled LDPE were discussed in our previous work (Akinay and Tincer, 1999). It already has been shown that silane coupling agents (SCAs) result in improvements in mechanical properties. The UV stability of these samples was followed by a comparision between strain at break measured after UV irradiation and the initial strain at break, in terms of their ratio defined as residual elongation. The development of carbonyl index was also determined by infrared measurements. To get further UV stability, a hindered amine light stabilizer (HALS) was also used. Whereas addition of 2 degrees-PTFE slightly enhanced the UV stability of LDPE, mercapto type silane (A-189) treatment appeared to increase the UV stability compared with the other types of silane treatments. HALS highly improved the UV stability of untreated and silane-treated 2 degrees-PTFE-filled LDPE at given UV irradiation time. Although we observed some fluctuations in the experimental data of HALS and SCA treated 2 degrees-PTFE-filled LDPE, the coaddition of HALS and SCAs showed synergetics effects in the UV stability compared with the separate additions. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 877-888, 1999.