Bulk metallic glasses (BMGs) have potential applications due to their Newtonian viscous formability between the glass transition temperature T-g and crystallisation temperature T-x and because of their high elastic strain range of about 2% below T-g. Among various metallic glasses however, some are more brittle in nature. Fe-based metallic glasses and some others are prone to thermal embrittlement even during the quench. This occurs when the critical applied load required for propagation of cracks is below that for inducing plastic flow at the testing temperature. Higher metalloid contents are needed to obtain bulk Fe-based metallic glasses but such increase in metalloid content also leads to embrittlement of the glass. It is shown that lower metalloid contents lead to reduced ductile to brittle transition temperaturs Tdb due to contributions from structural free volume. However, the reduced metalloid contents needed for ductile behavious increase the critical cooling required for glass formation. Fe-based BMGs are of most interest for their magnetic properties and brittle mechanical behavious is not a major obstacle to applications based on magnetic properties. Nevertheless it may be possible to obtain ductile Fe-based BMG-crystalline phase composites for thermodynamically selected compositions..