Previously, it was observed that secondary metabolites production was greatly enhanced by an artificial acidic pH shock in S. coelicolor A3(2) culture. The objective of this study was to examine the variation of intracellular protein expression in S. coelicolor A3(2) in response to an acidic pH shock. S. coelicolor A3(2) was cultivated on a solid medium (SMMS) under three different pH control conditions: positive control with no pH buffer (spontaneous pH drop and recovery); negative control with TES buffer; and culture with pH shock. Bacterial proteome was analyzed by two-dimensional gel electrophoresis. It was observed that 49 proteins were expressed at significantly different levels according to the culture conditions. These proteins were identified by peptide mass fingerprinting with matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Induced by the pH shock were proteins involved in energy metabolism (glycolysis, pentose phosphate pathway and TCA cycle), polyketide biosynthesis, degradation of macromolecules (polysaccharides, fatty acids, misfolded proteins) and histidine biosynthesis, ribosomal proteins, and proteins related to osmotic and oxidative stresses. Some of them were also expressed in the positive control: glycolytic proteins; ribosomal proteins; osmotic stress proteins; and oxidative stress proteins. Repressed by pH shock were proteins involved in glutamate transport, molybdenum cofactor biosynthesis, methionine metabolism, lysine metabolism, fatty acid biosynthesid, nucleotide biosynthesis, and MarR-family regulation. These results provided evidence, although indirect, that the artificial pH shock in the culture of S. coelicolor enhanced the productivity of secondary metabolites as a result of activation of several metabolic pathways such as pentose phosphate pathway and polyketides biosynthesis.