The alkaline-earth copper oxides Sr1-xCaxCuO2 (0 less than or equal to x less than or equal to 1) have been synthesized in flowing gas of N-2 or O-2 by thermal decomposition of hydroxide precursors Sr1-xCaxCu(OH)(4) . H2O. In the first step, we have succeeded in obtaining hydroxide precursors Sr1-xCaxCu(OH)(4) . H2O with 0 less than or equal to x less than or equal to 1 in the form of a precipitation in a highly concentrated NaOH solution. In the second step, namely, in the process of thermal decomposition, the hydroxide precursors have been found to be decomposed into an amorphous condition at a temperature as low as 200 degrees C. The ambient-pressure phase of SrCuO2 is obtained by heating the hydroxide precursors for 12 h at 500 degrees C and 700 degrees C in flowing gas of N-2 and O-2, respectively. The reaction temperature is much lower than the 1000 degrees C in flowing gas of O-2 in the conventional solid-state reaction method. With increasing x up to 0.7, the temperature at which the ambient-pressure phase of Sr1-xCaxCuO2 appears increases in flowing gas of both N-2 and O-2. The so-called infinite-layer compound of Sr1-xCaxCuO2 is obtained in a narrow ranee of x around 0.9 at similar to 1000 degrees C in flowing gas of O-2, which is similar to the result in the conventional solid-state reaction method. For x similar to 1, the ambient-pressure phase of Ca1-yCuO2 (y similar to 0.15) appears in the temperature range between 600 degrees C and 800 degrees C only in flowing gas of O-2.