The oily particles pose a threat to human health. To quantify the transmission of oily particles for developing mitigation strategy, the possible particle volatilization, adhesion and coagulation during air transmission and the water content of oily particles should be determined. Therefore, the particle size distributions at and away from the emission source were measured in the laboratory. Then, to further verify the results obtained in the laboratory, the particle size distributions of oily particles in a machining workshop were measured. Meanwhile, this investigation measured the water content of the oily particles in the machining workshop. The results revealed the evolution of particle size distribution of oily particles during air transmission could be ignored. The oily particles in the air had a water content of 22.6% and they were difficult to volatilize. The oily particles in the air might mainly consist of pure oily particles and water-in-oil particles.