In this study, carbon black (CB) was used to control the conductivity and the compatibility of immiscible poly(butylene succinate)/polylactide (PBS/PLA) blend. It is shown that most of the CB particles are selectively dispersed in the matrix PBS phase because of the viscosity ratio of the blend components. The increasing viscosity of PBS phase prevents the coalescence of the dispersed PLA domain during the melt mixing. The domain sizes of PLA are refined when compared with that of blank PBS/PLA blend. The ternary composite shows an onset of the electrical conductivity at low filler loadings (1.5 wt %), which is attributed to a percolation of CB in the insulating matrix polymer. Moreover, the composites exhibited remarkable improvement of rheological properties in the melt state when compared with that of blank PBS/PLA blend. According to the van Gurp-Palmen plot, the rheological percolation threshold for ternary systems is lower than 1.5 wt %. Furthermore, the ternary composites present improved mechanical properties and thermal stability even at very low loading levels of the CB. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012