Ship-based emissions have the potential to adversely affect both the environment and human health. The particulate component of exhaust emissions is especially dangerous as it can cause cardiopulmonary disease and lung cancer as well as respiratory illnesses such as bronchitis, asthma and pneumonia depending on the size, shape and chemical activity of the particles. For this study, experiments were conducted to investigate the particulate emissions from a medium-speed diesel engine installed on a ferry. The experiments themselves were focused on the effects of ultra-low sulfur diesel fuel on the formation of particulate emissions. The measurements of particulate matter and gaseous emissions were carried out on-board a ferry operating in the Marmara Sea. The size distributions of particle mass were obtained for different engine loads and a particle size of PM2.5 was found to be the most widespread under all engine loads. In terms of shape, the particles were found to be generally spherical. The composition of the particles was investigated by using SEM/EDX analysis. The elemental analysis of the particles revealed that the samples contained 13 elements. Carbon was found to be the main component of diesel particles, and accounted for approximately 50-60% of the total emission composition. Concentrations of Fe and V were also found to be abundant, accounting for approximately 8% of the total emission composition. The study also presents the emission factors for particulate matter (PM), as well as NOx, SO2, CO, CO2 and HC. The total of weighted PM emissions was found to be quite low at 0.079 g/kWh.