Dust generation from pig feed (maize/soybean meal diet) treated with soybean oil was investigated using a cement mixer in a plywood box. Airborne total dust concentrations in the box were measured gravimetrically using a vacuum pump and filters while 12-kg feed samples were constantly mixed. Treatment factors were soybean oil concentration (0, 1 and 3%), maize bulk density (normal, 730 and low, 600 kg/m3), time of oil addition (before or after grinding the maize), and storage time (0, 7 and 14 days). The feed was a mixture of soybean meal, base mix and adjusted amounts of ground maize and soybean oil. Total dust generation from feeds made with normal-bulk density maize was 29.1, 3.39 and 0.99 mg/m3, respectively, for 0, 1 and 3% soybean oil added after grinding. Adding soybean oil after grinding suppressed dust generation more than adding the oil before grinding at every oil level (P<0.001). More dust was generated by feeds made from low-bulk density maize at every oil level. Storage time or treatment X storage time interactions were not observed.