  Single crystals of the filled-skutterudite compound NdOs$_4$Sb$_{12}$ have
been investigated by means of electrical resistivity, magnetization, and
specific heat measurements. The NdOs$_4$Sb$_{12}$ crystals have the
LaFe$_4$P$_{12}$-type cubic structure with a lattice parameter of 9.3 \AA.
Possible heavy-fermion behavior is inferred from specific heat measurements,
which reveal a large electronic specific heat coefficient $\gamma \approx 520$
mJ/mol-K$^2$, corresponding to an effective mass $m^* \sim$ 98 $m_e$. Features
related to a ferromagnetic transition at {$\sim$ 0.9 K} can be observed in
electrical resistivity, magnetization and specific heat. Conventional
Arrott-plot analysis indicates that NdOs$_4$Sb$_{12}$ conforms to mean-field
ferromagnetism.
