  We study $N=(2,4,8)$ supersymmetric extensions of the three dimensional BMS
algebra (BMS$_3$) with most generic possible central extensions. We find that
$N$-extended supersymmetric BMS$_3$ algebras can be derived by a suitable
contraction of two copies of the extended superconformal algebras. Extended
algebras from all the consistent contractions are obtained by scaling
left-moving and right-moving supersymmetry generators symmetrically, while
Virasoro and R-symmetry generators are scaled asymmetrically. On the way, we
find that the BMS/GCA correspondence does not in general hold for
supersymmetric systems. Using the $\beta$-$\gamma$ and the ${\mathfrak
b}$-${\mathfrak c}$ systems, we construct free field realisations of all the
extended super-BMS$_3$ algebras.
