Since the mid-1990s, light-duty vehicles equipped with gasoline direct injection (GDI) engines have been added to the vehicle fleet in increasing numbers. Compared to conventional port fuel injection (PFI) engines, GDI engines provide higher power output for the same size engine, higher fuel efficiency, and lower carbon dioxide (CO₂) emissions. Due to the paucity of particulate matter (PM) emission data for light-duty gasoline vehicles in general and the increasing interest in these emissions relative to climate and air quality concerns, it is important to investigate PM emissions from current-generation GDI technologies. In this study, nine 2007-2010 light-duty GDI vehicles equipped with either wall-guided or spray-guided fuel injection systems were tested using California commercial gasoline fuel containing six percent ethanol by volume. Criteria pollutants including gaseous and PM emissions were measured over the Federal Test Procedure (FTP) transient test cycle. Two real-time particle measurement systems were utilized to measure solid and total particle number emissions.Test results show that PM emissions for first-generation GDI vehicles tested are significantly higher than PFI vehicles certified to California Low Emission Vehicle (LEV) II standards. In phase 1 of the FTP cycle during engine cold-start, PM mass emissions for the nine GDI vehicles ranged from 4 to 35 mg/mi, with an average of 14 mg/mi. The average FTP-weighted PM emissions for these GDI vehicles are 10 times higher than LEV II PFI vehicles tested previously. Over the FTP cycle, particle size distribution is bi-modal for the spray-guided GDI vehicle, and accumulation mode particles dominate particle emissions for the wall-guided GDI vehicle.