The political assistant to Chief Secretary Carrie Lam Cheng Yuet-ngor, the second-highest ranking member of the government, is stepping down.
She is the third political assistant to resign in a month.
Carmen Cheung Sau-lai cited "family reasons" for her decision to stop working for Lam, who plays a key role in contentious policy issues including poverty alleviation and electoral reform.
A government spokesman said Cheung, a former political editor at The Standard and public relations executive, had tendered her resignation "due to her need to take care of her family and will leave the government with effect from November 1", exactly a year after she took up the job.
Lam thanked Cheung for her contribution during her time in the role.
Cheung told Cable TV she was worried about her mother, who had been having health issues since March, and had no problem working with Lam.
"We have a good relationship, so there is no need for speculation," Cheung said. "If I thought the kitchen was getting too hot, I could have left much earlier."
Last month, Henry Ho Kin-chung, political assistant to much-criticised Secretary for Development Paul Chan Mo-po, resigned after admitting he had failed to declare that his family owned land in Kwu Tung earmarked for the development of a new town.
About a week later, Zandra Mok Yee-tuen, political assistant to the city's labour and welfare chief, said she was quitting to take care of her two young children.
City University political scientist James Sung Lap-kung said that since political assistants were responsible for liaising with lawmakers and political groups, the post needed filling soon.
He suggested Cheung's departure would cast further doubt over the cohesion of Chief Executive Leung Chun-ying's cabinet.
As chief secretary, Lam is responsible for assisting Leung in supervising the work of at least nine bureaus and ensuring co-ordination in policy formulation and implementation.