Post-dispersal seed predation is an important source of mortality in plant populations. If this phenomenon is better known in tropical and woody systems, information is lacking for weeds in French agrosystems. In this paper, we evaluated seed predation variability in an organic wheat field by conducting experiments on weed seed preference and on spatial and temporal variation in predation rates. Weed seed predation preferences followed a species rank: Viola arvensis = Stellaria media > Alopecurus myosuroides = Chenopodium album > Sinapis arvensis = Anagallis arvensis = Galium aparine > > Plastic globules (for control), with weekly mean predation rates between 19 and 84%. The experiment on spatial variation in seed predation did not reveal a field border edge effect on predation rate with S. arvensis. However, a strong temporal variability has been found within a single season. Simple seeds characteristics as well as meteorological conditions were not directly correlated to predation rates obtained. High predation rates observed here underline the potential importance of this phenomenon on weed population dynamics. A future challenge would be to quantify the impact of post-dispersal seed predation on weed communities in order to assess the potential of seed predation for biological weed management.