PHA-based nano-biocomposites have been prepared by melt intercalation. Two main PHAs, poly(hydroxybutyrate) and poly(hydroxybutyrate-co-hydroxyvalerate) have been studied. Structural characterizations were conducted by advanced techniques like SAXS and TEM. A recent method has determined the degree of clay intercalation and dispersion using solid-state NMR. Well intercalated small tactoids (3–10 layers) homogeneously dispersed into the polymer are obtained when good PHA–clay affinity exists, i.e., with organo-modified MMT. In the case of non-modified MMT, microcomposites are evidenced. Crystallization, mechanical, and thermal properties have been correlated to the materials structures.