The phrase "a modest demeanor" is correct and usable in written English.
It can be used to describe someone who presents themselves in a humble or unassuming manner.
Example: "Despite her numerous achievements, she maintained a modest demeanor that endeared her to her colleagues."
Alternatives: "a humble attitude" or "an unpretentious manner."
A very good, ultraflat apple tart, topped with little dabs of pecan cream, has a modest demeanor but a very big flavor.
With a pronounced forehead, wide-set, deeply sad eyes and a modest demeanor, Mavado didn't always stand out in this crowd.
The lady who hired him for Macy's remembered him well and described him a "thoroughly wholesome, typical American boy, with a deep wave in his hair, a ruddy complexion, keen eyes, erect bearing, and a modest demeanor.
During the hullaballoo over the spy story, a personnel employee at Macy's in Herald Square who had hired Mr. Cullen as a deliveryman's helper before his Coast Guard enlistment described him to The New Yorker as "a thoroughly wholesome, typically American boy" with "a modest demeanor".
A man of modest demeanor, Dwight D. Eisenhower took shelter behind a small army of surrogates as presidential lightning rods.
A warm and kind person, her positive attitude and modest demeanor made her a role model to those who had the good fortune of knowing her.
"I'm going to brag a bit," said Mr. Nahas, whose modest demeanor belied these words.
When you speak up, do so with civility, with knowledge of local history and local values and with the modest demeanor appropriate to a visitor to another country.
A former chairman of Harvard University's Graduate School of Design, he has a modest, thoughtful demeanor.
Mr. Babbitt, 74, whose modest demeanor masked the sharpness of his critique of a fellow Democrat, said in a speech at the National Press Club that Mr. Obama was falling behind many of his predecessors in setting aside lands for wilderness while making vast tracts available for drilling.
In conversations about Beaton and Hockney, she saw a sensibility that she loved -- and soon discovered, happily, that his modest demeanor contained northern flint.
