Magnetic circular dichroism (MCD) was measured at Langmuir-Blodgett films of magnetite (Fe3O4) nanocrystals. The measurements of the effect were preformed in two different configurations, transmission and reflection. When a nanocrystal monolayer was deposited on a rough gold surface, the MCD signal was enhanced significantly in comparison to the signal obtained for a monolayer deposited on a hydrophobic glass substrate. The effect was found to be sharply dependent on the separation distance of the magnetite monolayer from the gold surface. This surface enhanced magnetooptical (SEMO) effect is probably caused by the enhancement of the electric field component of the electromagnetic waves at rough features of the gold surface.