Ozawa became acquainted with adult videos (AV) by watching sex tapes she borrowed from a friend's brother. Unlike most AV actresses, Ozawa was not scouted. Instead, she was introduced to the AV industry through a friend appearing in AVs.She began by modeling as Miyabi for the pornographic site Shirouto-Teien.com in June 2005, which resulted in several sets of photographs and a short hardcore gonzo video released in CD-R and DVD-R formats.
She was then signed by S1 No. 1 Style, an AV studio that produces light hardcore pornography. On October 7, 2005, she premiered as Maria Ozawa with the video New Face – Number One Style (新人xギリモザ ナンバーワンスタイル), directed by Hideto Aki. Ozawa remembers that she was so nervous during the filming of her first AV that she could not look the male actor in the face. At S1, Ozawa subsequently appeared in one original video per month until February 2007. She was involved in several S1 compilation videos including the company’s entry in the 2006AV Open, a competition between Japanese AV studios for the best selling video. The S1 video Hyper – Barely There Mosaic (ハイパーギリギリモザイク), featuring Ozawa along with other AV idolsSora Aoi, Yua Aida, Yuma Asami, and Honoka (plus a short preview for Rin Aoki), won first place.
Ozawa and S1 parted ways in early 2007. Along with Rin Suzuka, Reina Matsushima and Rin Aoki, she moved from S1 with its emphasis on glamour to a new start-up company, DAS, which featured scenes of creampie and simulated rape. On April 25, 2007, DAS released their first videos, one of which (Beautiful Eurasian News Anchor Maria Ozawa Desiring Nakadashi Rape) featured Maria Ozawa. By the end of 2007, she signed (not exclusively) with Attackers (アタッカーズ), an established AV studio that specializes in thematic rape pornography.
Besides adult videos, she has appeared in V-Cinema films, a photobook and several glamour ("gravure") videos. In 2007, she played the character Anita (ｱﾆｰﾀ) on the popular Japanese TV drama Tokumei Kakarichō Tadano Hitoshi (特命係長・只野仁) on TV Asahi. In addition, Ozawa was on a 2007 episode of the Japanese variety show Megami no hatena ("The Goddess of What Is That") on Nihon TV as part of a series with AV actresses telling why they went into AV work. She has also appeared on Japanese MTV with the hip hop artist Seamo and in the 2007music video Summer Time in the D.S.C. with the Yokohama hip hop group DS455.Ozawa could be seen in 2007 performing twice at the Shinjuku striptease bar "Shinjuku New Art". She took dance lessons to prepare but was still very nervous. She danced in a variety of outfits including appearing as a belly-dancer, a geisha and a cowgirl. Three videos were released of her performance and a behind-the-scenes interview.