We have prepared new perovskite manganites La 0.7 Ca 0.3− x K x MnO 3 (0⩽x⩽0.15). These compounds are shown to undergo structural transition from orthorhombic to rhombohedral phase. When increasing x, the structural properties reveal the existence of a stronger disorder, for the orthorhombic structure, which leads to an increase of the Mn–O–Mn bond angle and a decrease of the Mn–O bond length. This behaviour contributes to the increase of the one-electron bandwidth W, which results in an increase of the Curie temperature T C . For the rhombohedral structure, the disorder is suppressed, so W and T C decrease. The Raman studies at 300K indicate that the spectra of La 0.7 Ca 0.3− x K x MnO 3 are modified when x increases. The strong x dependence of the phonon linewidth suggests that considerable lattice disorder is already present which confirms the structural transition observed by X-ray diffraction patterns.