We report here the magnetic ground state in the hole-doped two-leg ladder system Sr2.5Ca11.5Cu24O41 at ambient pressure. We clearly observed the singlet ground state, of which values are almost unchanged for the different Ca concentration (similar to 32 meV). We also observed the antiferromagnetic long-range order below T-N of which values are between similar to0.6 K (x = 9) and similar to 3.6 K (x = 1.36). A possible magnetic structure of this system, was also discussed. These facts can be interpreted in line with scenario that the singlet state and antiferromagnetic order coexist at ambient pressure and these localized hole pairs begin to move under pressure, resulting in the occurrence of superconductivity, (C) 2000 Elsevier Science Ltd. All rights reserved.