Abstract The liquid extraction of some lanthanides (Pr, Gd, and Yb) with mixtures of heptanoic acid H3C(CH2)5COOH (HA) and crown ethers (B) benzo‐15‐crown‐5 (B15C5), dicyclohexano‐18‐crown‐6 (DH18C6), and 18‐crown‐6 (18C6) in carbon tetrachloride (CCl4) as a solvent from aqueous chloride medium at constant ionic strength μ = 0.1 is investigated. A synergistic effect in the extraction of Pr, Gd, and Yb with B15C5 and antisynergistic effects in the systems containing the other two crown ethers DH18C6 and 18C6 are observed. For Pr, a formation of mixed complex Pr(HA2)3 · B15C5 is found and the corresponding equilibrium constant is reported, while Gd and Yb form the complexes Gd(HA2)3 · nB15C5 and Yb(HA2)3 · nB15C5, respectively, where n < 1.