In this paper we study the effect of combining the conducting polymers, P3HT and OC(1)C(10)-PPV with the fullerene complex PCBM, on its positron annihilation characteristics. The films were deposited on glass substrates by spin casting, and were also characterised with scanning electron microscopy with regard to thickness, and structural homogeneity. Both pure polymers have positron annihilation characteristics similar to most non-polar polymers, exhibiting a relatively broad electron momentum distribution, a long-lived (>1 ns) positron state corresponding to the formation of ortho-positronium, and strong-localisation of the positron. Mixing with PCBM causes the sampled electron momentum distribution to narrow, and results in a single annihilation state with a lifetime of around 370 ps in both polymer mixtures. We postulate that this state corresponds to annihilation with the low-momentum electrons in the fullerene cage.