Thermal conductivities of single-wall carbon nanotubes (SWNTs) filled with argon (Ar) with types (10, 10) and (15, 15) respectively, are calculated over a temperature range of 500-1200 K using equilibrium molecular dynamics (EMD) simulation method. The Tersoff potential for C-C bonding interactions and the Lennard-Jones (LJ) potential for Ar-C nonbonding interactions are employed. The effects of filled argon on the thermal conductivity of SWNTs as well as the temperature dependence of their thermal conductivities are investigated. It is found that the thermal conductivities of filled (10, 10) and (15, 15) SWNTs, showing qualitatively similar behavior to that of a bare unfilled nanotube, decrease as the temperature increases. Moreover, it is demonstrated that the thermal conductivity of nanotubes filled with argon is much higher than that of an empty nanotube at all temperatures. This increase is perhaps attributed to the heat transfer derived from the Ar-nanotube interaction, and the mass transport due to the active movement of the Ar atom in SWNTs