Dawn Smith, deputy editor of Natmags' Real People, has resigned three months after launch editor Vicky Mayer left the title.
ACP-Natmag chief executive Colin Morrison said: "This is unprompted and regretted. Dawn's done a really good job for us. The magazine's doing very well and we're pleased with what she's done."
Real People poached Smith from Bauer title That's Life!, where she was deputy editor.
Mayer, who left at the end of May, is now deputy editor on Emap's news weekly, First, a role a spokeswoman for Emap said was "not a permanent arrangement".
ACP-Natmag is still looking to recruit a new editor for Real People, but Morrison declined to put a timetable on this.
Editorial director Louise Court is acting editor and former Chat editor Terri Tavner is working as a freelance editorial consultant.
ACP-Natmag is currently spending £2m on Real People's TV advertising campaign.
It has added a 16-page puzzle book to the title, which now has weekly prize money of more than £80,000, which Morrison claimed was "the biggest in the market".
Real People, which launched in January last year, reached its sales target with a figure of 318,105 in its first ABCs last month.