Four new azo compounds namely, 2-(sec-butyl)-4-((4-methoxyphenyl)diazenyl) phenyl-4-(hexyloxy)benzoate (I6(a)), 2-(sec-butyl)-4-(p-tolyldiazenyl)phenyl-4-(hexyloxy) benzoate (I6(b)), 4-((4-bromophenyl)diazenyl)-2-(sec-butyl)phenyl 4-(hexyloxy)benzoate (I6(c)) and 2-(sec-butyl)-4-((4-nitrophenyl)diazenyl)phenyl 4-(hexyloxy)benzoate (I6(d)) were synthesized. Their structure elucidated via Elemental Analysis, FT-IR, H-1-NMR and Mass Spectroscopy. Their mesophase behavior was investigated by Differential Scanning Calorimetry (DSC). They were tested as antioxidants for local base oil. The efficiency of them was investigated via monitoring the oxidation reaction through the change in total acid number (TAN) and viscosity. The obtained results showed that, the efficiency of these compounds was ranked as follows I6(d) > I6(c) > I6(b) > I6(a).