The self-recognition between oppositely charged polyelectrolyte-neutral diblock copolymers and aggregate formation is investigated by Monte Carlo simulations. Both matched lengths and charge numbers are critical conditions for self-recognition. The optimum self-recognition occurs between oppositely charged chains with matched charged block lengths and charge numbers. The size of aggregates increases, as the total length and the ratio of charged to neutral beads become larger. Polyelectrolyte networks were observed in some cases containing unmatched chains. The molecular configurations of the entire chains and of the charged and neutral blocks as well as the radial distribution functions of the charged beads are also investigated.