De Blasio, a left-leaning Democrat who supported Hillary Clinton, has expressed outrage over Trump's plan to deport millions of undocumented immigrants.
"I reiterated to the President-elect that I would be open-minded as we continue these substantive discussions but that I will also be vigilant and swift to react any time an action is taken that undermine the people of New York City," de Blasio told reporters outside Trump Tower in Manhattan.
De Blasio told reporters he spoke to Trump as the voice of a city comprised largely of immigrants, who de Blasio said now live in fear of Trump's proposed plans on deportation and to ban Muslims from entering the country.
"I tried to express to him how much fear there is -- how much fear there is in communities all over this city," de Blasio told reporters. "A whole range of people in the biggest city in the country who are fearful about this current dynamic and how we need to see things that will give people more assurance that all New Yorkers and all Americans will be respected."
The mayor also expressed concern that large-scale deportations would "sew distrust" between law enforcement and communities.
Trump's former campaign manager, Kellyanne Conway, described the meeting to reporters outside Trump Tower as "very productive."
"I think they both said it was a very productive meeting and it lasted about an hour or so. I was glad that the mayor came here," Conway said.
She added that she wasn't sure who arranged the meeting, but "even when invitations are extended or suggested, it's up to President-elect Trump whether or not he accepts them, but he's very open and he's been talking to any number of people."
De Blasio would only tell reporters about issues he raised with the President-elect and would not characterize the tone of the meeting or Trump's responses.
Among the concerns de Blasio raised were his opposition to Trump appointing Steve Bannon, formerly the head of Breitbart News, as his chief strategist and senior counselor. Bannon's website has been accused of promoting white nationalism, racism, misogyny and anti-Semitism.
De Blasio said he also brought up Trump's promise to repeal the Dodd-Frank Act, a piece of legislation meant to reform Wall Street, saying he had "deep concern that we would go backward and that our economy would be in peril again and we would run the risk of another crash."
As the hour-long meeting was underway, across town there was a different move to distance New Yorkers from the President-elect: the removal of Trump's name
from three luxury apartment buildings he helped develop on the west side.