Lam's announcement came as media said Chief Secretary John Lee, Hong Kong's second most senior official, was set to resign to join the race to replace Lam in May as the Chinese-ruled city's next leader.
"There’s only one consideration and that is family. I have told everyone before that family is my first priority," Lam told a regular press briefing.
"They think it’s time for me to go home."
She declined to comment on possible candidates to replace her and said she had not decided on her future plans.