The London-based studio led by architect Norman Foster picked up the award for best overall website, described by judges as "a tour de force in making so much content accessible and easily navigable".
"This is a very polished and high quality website, as it should be, and communicates perfectly to the practice's broad international audience," said the judges.
The website, designed by digital studio AKQA, was also praised for its integration of multimedia.
"Technology is used in a restrained manner that reflects the firm's design ethos and the projects and information are beautifully presented with a fantastic level of detail," added one judge.
Foster + Partners also picked up the award for best use of video.
Dezeen is media partner for the Archiboo Web Awards, a London-based organisation set up by former BD editor Amanda Baillieu to spotlight architecture companies that are using the internet in a creative way.
The programme includes 10 awards, which cover visual design, user experience, use of technology and social media.
The award for best homepage was awarded to US firm Trahan Architects, for a design that judges said offered "a perfect balance of beauty, intrigue, information and functionality". The studio also won best use of digital imagery, thanks to renderings by The Boundary.
Meanwhile the prize for best visual design went to Heatherwick Studio for a new website, described as having a "distinctive and confident aesthetic which communicates a message that is recognisably relaxed and original but still good on detail".
Dezeen editor-in-chief Marcus Fairs was one of the judges for the prize for best written content. The prize was given to Jamie Fobert Architects, for a website with a "no nonsense approach with crisp, honest writing".
"The descriptions of the work have a nice, story-telling quality without too much jargon or too many warm words that lack real meaning," said one judge.
Dutch firm UNStudio picked up two awards, for best offline experience and best use of social media. One judge said the studio's "use of social media channels to convey office culture as part of the online identity of the practice is also very effective".
The other winners were Uniform, for best use of innovation, and Bennetts Associates, for best mobile experience.
The Archiboo Web Awards winners were announced in a ceremony during London Design Festival last week.
The programme is now in its third year. Last year, the prize for best website was awarded to London studio David Miller Architects.
In a column for Dezeen, Amanda Baillieu said she set up the awards to show that the internet offers a world of opportunities for architects.