Detailed characteristics of particulate matter (PM) from a gasoline-direct-injection (GDI) engine were analyzed in terms of primary and aggregate particle sizes, morphology, and nanostructures. For the work, PM was collected from exhaust streams of the engine on transmission electron microscope (TEM) grids by using a thermophoretic sampler. To evaluate the effects of engine load and speed on the properties of PM, the engine was operated at loads of 25, 50, and 75% at 1500 and 3000 rpm. In addition, the effects of fuel injection timing on the PM were examined for samples subjected to injection timings of 190, 230, 260, 300 and 330° bTDC at the constant engine load (50% load) and speed (1500 rpm).The results showed that with advancing injection timing, average primary and aggregate particle sizes gradually increased, which implies that fuel-air mixing is a crucial factor influencing particle size. In particular, an increased number of nano-particles smaller than 20 nm in dp and Rg at 190° bTDC were found. Fractal analysis showed that aggregates from the GDI engine reside in compactness in between those from light-duty diesel engines and from heavy-duty diesel engines.High-resolution TEM examinations revealed that PM from the GDI engine had less-ordered graphitic structures than from typical diesel engines. Also, it is noted that like soot derived with alcohol blends disclosed in our previous studies, certain particles produced at only 3000 rpm were observed to undergo particle expansion by exposing to a high-energy electron beam during TEM measurements, which has been rarely reported for diesel particles.