The formation and aggregation of the Pd(II) complex with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (HL) at the heptane-water interface was investigated by UV-vis absorption and resonance Raman spectrometry using the centrifugal liquid membrane (CLM) method. The interfacial aggregate had an absorption maximum wavelength at 488 nm, showing a hypsochromic shift from the absorption maximum wavelength at 580 nm of the complex monomer (PdLCl). The critical aggregation concentration of PdLCl was determined to be 2.6 × 10^-10 mol cm^-2. The observed UV-vis absorption and resonance Raman spectra implied that the ligand in the interfacial aggregate was mainly in the state of azo form, because the spectra were very similar to those of the PdLCl complex obtained in a low-polarity solvent such as toluene.