The regulator's Financial Services Register will experience an outage next week if the UK leaves the European Union on April 12.
In a statement on its website the Financial Conduct Authority confirmed the register would be unavailable because of maintenance from 11pm on April 12 and was expected to be down for three days.
The regulator apologised in advance "for any inconvenience caused" by the planned outage and confirmed the register would be live as soon as the works were completed.
The register would be updated to reflect changes required to companies' details in the event of Brexit, which an FCA spokeswoman said related to companies joining the regulator's temporary permissions regime and the necessary passporting permissions.
According to the FCA, the temporary permissions regime will allow companies which currently passport into the UK to continue operating in the country if the passporting regime "falls away abruptly" after Brexit.
Last week the FCA published its final rules for a no-deal Brexit, including an extension to the notification window for companies who wish to join the regulator's post-Brexit regime.
Unless the House of Commons approves prime minister Theresa May's deal or the EU agrees to a further extension, the UK will leave the bloc on April 12 without a deal.
If the deal is approved, the EU has agreed to extend the UK's membership until May 22 to allow for the deal's implementation.
Since MPs have so far rejected Theresa May's deal three times, the UK would leave the EU without a deal on April 12 but Mrs May has now sought a further extension until June 30.