La1-zNdzFe4−xCoxSb12 skutterudites were prepared by using melting, quenching, annealing, and hot pressing. The major phase was the skutterudite phase but small amounts of FeSb2 phases were observed. In addition, especially for the Co-compensated specimens (x = 0.5), (La,Nd)Sb2 phases existed. The electrical conductivity decreased with increasing temperature, showing a degenerate semiconductor behavior. The electrical conductivity decreased with increasing La and Co contents due to a decrease in the carrier concentration. All specimens showed p-type characteristics, having positive signs of the Seebeck coefficient and the Hall coefficient. The Seebeck coefficient increased with increasing temperature and reached a maximum value at 823 K. The power factor (PF) increased with decreasing Co content, and La0.75Nd0.25Fe4Sb12 showed a peak value of the PF = 3.0 m Wm-1 K2 at 823 K. The electronic thermal conductivity decreased with increasing Co content, and for a fixed Co content, the lattice thermal conductivity decreased with increasing filling fraction of Nd. The thermal conductivity increased due to bipolar conduction at temperatures above 623 K. The dimensionless figure of merit (ZT) had a maximum value of ZT = 0.82 at 823 K for La0.75Nd0.25Fe4Sb12.