Surface tension data for the system comprising of nitrobenzene and fused tetra-n-butyl ammonium picrate have been collected at 364.1, 373.1, 383.1 and 393.1 K for compositions ranging from pure fused tetra-n-butyl ammonium picrate to nitrobenzene. These surface tension values are combined with our earlier published solvent activity data in order to calculate the surface activities of the system. The experimental results on the surface tension have been analyzed in terms of a newly proposed two-parameter equation with an average r.m.s.d. of 0.024 x 10(-3) N m(-1). An attempt has also been made to predict the shape of non-ideal surface tension term vs. composition curve using the Scaled Particle Theory.