Recently, via-filling plating used build-up processes has been an active topic of study. Generally, polyethylene glycol 4000 (PEG4000) has been used as a carrier with a wide concentration range of 100-1000 ppm. In addition, Bis-(sodium sulfopropyl)-disulfide (SPS) is used as a brightener with a very narrow concentration range of 1-10 ppm. The concentration of additives is considered to affect via-filling plating strongly. However, no simple analytical method has been reported for these additives. This study analyzes the concentrations of PEG4000 and SPS in a simulated plating bath. These additives were analyzed using a high-performance liquid chromatography (HPLC) system incorporating boron-doped diamond (BDD) as the electrochemical detection electrode material. Results show that PEG4000 and SPS in the simulated plating bath were detectable in separation. The correlation coefficients between added concentration and peak currents were 0.988 for PEG4000 and 0.999 for SPS.