During pathogenesis, the ascomycete Botrytis cinerea secretes a range of cell-wall-degrading enzymes such as polygalacturonases, glucanases and proteases. We report the identification of a new member of the G1 family of proteases, BcACP1, which is secreted by B. cinerea during infection. The production of BcACP1 correlates with the acidification of the plant tissue, and transcriptional analysis of the Bcacp1 gene showed that it is only expressed under acidic growth conditions. Using a transcriptional reporter system, we showed that pH regulation of Bcacp1 is not mediated by the canonical PacC transcription factor binding site. Like other G1 proteases, BcACP1 is produced as a pro-enzyme. Trapping of the zymogen form allowed investigation of its maturation process. Evidence is presented for an autocatalytic proteolysis of the enzyme that is triggered by acidic pH. Environmental pH therefore controls Bcacp1 production at both the transcriptional and post-translational level.