Engine oil, as a multifunctional compound plays an important role in engine performance, which maintains their qualitative properties. The quality of engine oil decreases with increasing engine operation and must be replaced. Entrance of sand dust in lubrication system through the intake manifold, degrades the engine oil quality and increases the engine wear. Operation of agricultural tractors makes a lot of air dust including silica and calcite. In the present study, the effect of calcite and silica particle on the quality of engine oil (Sepahan Oil, API SC-CC SAE 40) and the metal wear of engine parts were investigated. The presence and particle size of silica and calcite in the engine oil were determined by X-ray diffraction (XRD), and scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively by sampling from tractors working in the fields of eastern Isfahan. Three levels of silica and calcite content (1, 2, and 3 g/L) were used based on the amount of silica and calcite in the engine oil of the tractors with the particle sizes of less than 1 and 40 µm, respectively. The silica and calcite particles were added to the oil and the some quality properties of the oil and wear particles were measured after 20 hours of the engine operation. The results showed viscosity, density, and the pour point of the engine oil were significantly ( P 0.05) enhanced with the increase in the silica content. However, no significant change was observed in the engine oil flash point. When 1, 2, and 3 g/L of silica particles were added to the engine oil, viscosity at 40 °C was increased by 3.2%, 5.9%, and 3.6%, respectively compared to no contaminated oil. By adding 3 g/L of silica to the engine oil, the oil density increased significantly to 9.224 g/cm 3 . The oil pour point was changed by 24%, 8.5%, and 15.5% using 1, 2, and 3 g/L of silica was added to the engine oil, respectively compared to no contaminated oil. The calcite particles, except for the oil flash point, did not have any significant effects on the oil quality after 20 hours of the engine operation. The flash point of engine oil after adding 1, 2, and 3 g/L of calcite to the engine oil was 243.33, 250.67, and 238 °C, respectively. In 1, 2, and 3 g/L of the silica content of the engine oil, there were 136.7, 176.3, and 1758.6 mg/L of iron particles, 27.38, 46.65 and 47.85 mg/L of aluminum particles, and 3.54, 5.85, and 10.73 mg/L of chromium particles, respectively. In addition, the number of copper, nickel, lead, manganese and bismuth particles of the engine oil increased with increasing silica values. The calcite particles, except for aluminum and copper, did not have any significant effects on the wear of other engine parts. It seems that a larger amount of calcite can block engine oil channels, reduce the thickness of oil films‌, and consequently increase friction between and wear of engine moving parts. With increasing silica and calcite particles in the engine oil, no significant change was observed in the engine oil oxidation after 20 hours of engine operation. Thus, the quality of filters in agricultural tractors is to be improved to prevent silica and calcites of dust enter. Key Words : Engine oil, Dust, Viscosity, Flash point, Pour point, Density, Engine wear.