In this work, detailed physicochemical characteristics of particulate emissions were investigated over ranges of fuel properties, particles size distribution, chemical compositions and toxicity based on dynamometry experiments with marine diesel engines. The results indicated that lower fuel sulfur content (FSC) can decrease the specific emissions of total particle matters (PM). Organic carbon (OC) emissions were more than elemental carbon (EC), especially for 2-stroke marine diesel engine with heavy fuel oil (HFO), and carbonaceous substances were found to be load and size dependent. The suppression effect of low-sulfur light diesel fuel (LSDF/DF) for PM mass emissions was exhibited mostly in the reduction of OC and sulfate, compared with high-sulfur light diesel fuel (HSDF). PM mass emissions with low-sulfur HFO were still higher due to larger OC emissions. Emissions of 16 priority polycyclic aromatic hydrocarbons (PAHs) were highest in particle-phase PAHs, among which 3 and 4-benzene ring PAHs were predominant. Flua and Pyr were the PAHs with the highest emissions in the PM emitted from marine diesel engines. The PAHs had very high toxic equivalent, with the highest contribution of BaP and DahA. According to benzene rings number, the proportion of 5-benzene ring PAHs had the highest equivalent toxic concentration. Size distribution of PAHs had high correlations with OC and the PM with small size had higher equivalent toxicity concentration.