We present a study of charge transfer in polyfluorene: [6,6]-phenyl C 61-butyric acid methyl ester (PCBM) blend films. After photoexciting the conjugated polymer, electrons are very quickly transferred onto the PCBM leaving positive charges in the polymer. The presence of new photogenerated species in both polymer and PCBM can be demonstrated by photoinduced optical absorption studies. Using ultrafast spectroscopic experiments, not only are we able to demonstrate the charge transferprocess in such composites but also we can time resolve the dynamics of the process. Charge transfer is, in this way, estimated to take place ∼4 ps after photoexcitation. After ∼120 ps all charges have already been transferred and the process concludes. The resulting separated charges have the potential to produce a photocurrent if they are successfully driven through the bulk and collected by suitable electrodes.