The B-stage of the o-cresol novolac epoxy resin-phenol novolac hardcner-triphenylphosphine (TPP) catalyst system was characterized using Raman spectroscopy and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The consistent decreasing intensities of characteristic epoxy resin peaks in MALDI mass and Raman spectra according to the melt mixing time were observed, which is due to the formation of the epoxy-phenol-TPP complex and the propagation reaction between them and with another epoxy resin. Our microscopic analysis method will provide a useful tool to control the optimum condition of the melt mixing process in the B-stage.