Abstract: Here, we studied the effects of landscape complexity on the host plant-aphidparasitoidsystem, parasitoid species diversity and parasitism rates in 12 alfalfa fields in thesurroundings of Belgrade, Serbia. Sampling was done during two different plant phenophases(the stage of early and late bud) throughout the alfalfa vegetative season (April to October) in2010. Landscape complexity was measured as the percentage of non-crop area in 1.5km diametercircular landscape sectors around the sampling plots. Our results demonstrate that landscapecomplexity had no effect on aphid parasitoid species diversity and rates of parasitism decreasedsignificantly in complex landscapes. This finding suggests that complex landscapes supportedhigher aphid densities, but not higher parasitoid densities, resulting in overall higher parasitismrates in simple vs. complex landscapes.