A new Cu-La-Zn alloy system with high thermal conductivity was developed for die casting, and the thermal conductivity of this alloy system was 200-300 W/(m·K), which was twice as that of ordinary brass. The effects of Cu₆La intermetallic compounds and Zn solute atoms on the strengthening and thermal conductivity behaviors were quantitatively studied in as-cast binary Cu-La (2.0-4.5 wt.% La) and ternary Cu-2La-xZn (0-3.0 wt.% Zn) alloys, respectively. The results showed that for the increase of per 1 wt.% La or Zn, the thermal conductivity decreased by about 34 W/(m·K). In Cu-2La-xZn alloys, the lattice constant of α-Cu matrix increased from 3.6163 to 3.6239 ？. Due to the solid solution strengthening of Zn atoms, the hardness of the α-Cu matrix showed a parabolically increasing tendency, from 1.495 to 1.597 GPa. According to the calculations of the Maxwell-Eucken model based on the microstructure, the thermal conductivity of Cu₆La phase was determined to be about 35.37 W/(m·K), and the reduction in thermal conductivity of α-Cu matrix caused by Zn solute atoms was quantified to be 51.38 W/(m·K) per 1.0 at.% Zn increase.