The authors report a mechanism of interfacial strengthening during creep deformation of fully lamellar TiAl alloys. In the lamellar microstructure of TiAl alloys, the ��2 phase or the �� phase is softer than the �� phase at elevated temperature. Conventionally, the creep resistance increases with decreasing the volume fraction of the soft phases. However, the lamellar interfaces of �� ��2 or ���� retard the motion of dislocations during creep, causing a great strengthening, and thus the creep resistance increases with increasing the amount of the phase interfaces. In this study, a physically based model is developed to explain the strengthening behavior of the soft phases in lamellar TiAl alloys. �� 2007 American Institute of Physics.