Swaged Mo-

x

La

2

O

3

alloys (

x

 = 0

0.3

and 0.6 wt.%) were subjected to different annealing temperatures (

T

a

)

in order to demonstrate the

T

a

-sensitive La

2

O

3

effect on microstructural evolution and tensile ductility. Although coarse La

2

O

3

particles were detrimental to ductility

nanosized La

2

O

3

particles were found to increase the ductility by highly stabilizing the deformation-induced hierarchical microstructures of lamellar elongated grains with low-angle grain boundaries inside. A competition between the two opposite effects derived from the La

2

O

3

addition led to an unexpected

x

-dependence of ductility upon different

T

a

.