The development and selection of a morphological variant were systematically observed during continuous cultures of Aspergillus oryzae A1560 carried out at a dilution rate of 0.1 h−1. The selection was monitored by following the changes in the population morphology and in the α-amylase production during these experiments. A mathematical model for the selection was proposed assuming that the inoculum consisted of a mixed population. Growth, glucose uptake and α-amylase production for the selected morphological variant were further investigated in glucose-limited continuous cultures carried out at dilution rates ranging from 0.06 to 0.2 h−1. The selected variant was distinguished from the parental strain in three main aspects: (1) a higher capacity of α-amylase production at all dilution rates investigated; (2) a 36% higher maximum specific growth rate; and (3) a more sparsely branched mycelium, with fewer aerial hyphae and loss of sporulation ability on solid media.