Martins, grabbed the award after he saw off Landon Donovan of LA Galaxy, Diego Valeri of Portland Timbers, Steve Clark of Columbus Crew and Lee Nguyen of New England Revolution.
The former Inter Milan star grabbed five goals and one assist in five games in the month of September for the Rave Green.
The former Newcastle forward, pulled 58 of the poll votes by fans with his closet contender Donovan only garnering 13.56 percent of the vots.
The 29-year-old, has scored a total of 15 goals this season and notched up 10 assists in 23 MLS games for the MLS outfit.
Seattle Sounders are sitting atop of the Western Conference with 57 points from 23 games this season.
Final results for Etihad Airways Player of the Month (September)
Obafemi Martins (SEA) 58.43%
Landon Donovan (LA) 13.56%
Diego Valeri (POR) 12.17%
Steve Clark (CLB) 8.15%
Lee Nguyen (NE) 7.69%