In this study, transcriptional analyses by using reverse transcription-polymerase chain reaction (RT-PCR), DNA chip, and quantitative real time-PCR were performed to investigate effects of acidic pH shock on two-component systems in Streptomyces coelicolor A3(2). Two-component systems of cseC/cseB and vanS/vanR, known to be closely linked with self-protection against cell wall hydrolysis caused by external stimuli were upregulated by the pH shock. The chiS.chiR, afsQ2/afsQ1, ecrA2/ecrA1, bldM, ramC/ramR, and ragK/ragR known to be positively associated with the initiation of secondary metabolism were also upregulated. The AiipLAiio known to be negatively related to the secondary metabolism was, however, slightly downregulated. Upregulation or downregulation by the acidic pH shock of these two-component regulator systems might have contributed in a concerted manner to the enhancement of secondary metabolite production, at least, in this particular case of actinorhodin production in S. coelicolor A3(2).