Portevin-Le Chatelier (PLC) effect in a severely cold-rolled Al-Zn-Mg-Cu-Zr aluminum alloy (AA7055 type) plate before and after annealing was investigated. The results show that the sample annealed at 300 ℃ undergoes PLC effect, whereas the PLC effect is not observed in the deformed sample or the samples annealed at 110 ℃ or 200 ℃. The main precipitates in the sample annealed at 300 ℃ are the coarsened η phases, while a mixture of small η′ phases and η phases dominates in the sample annealed at 200 ℃. In the deformed sample and sample annealed at 110 ℃, GP zone are the main precipitates. The different flow behaviors are ascribed to the type of precipitates as well as the dislocation density differences.