We present an analysis of the high-resolution Chandra observation of the multiple system, HD 155555 (an RS Canum Venaticorum; RS CVn type binary system, HD 155555 AB, and its spatially resolved low-mass companion HD 155555 C). This is an intriguing system that shows properties of both an active pre-main-sequence star and a synchronized (main sequence) binary. We obtain the emission measure distribution, temperature structures, plasma densities, and abundances of this system and compare them with the coronal properties of other young/active stars. HD 155555 AB and HD 155555 C produce copious X-ray emission with log {L}{{x}} of 30.54 and 29.30, respectively, in the 0.3–6.0 keV energy band. The light curves of individual stars show variability on timescales of a few minutes to hours. We analyze the dispersed spectra and reconstruct the emission measure distribution using spectral line analysis. The resulting elemental abundances exhibit an inverse first ionization potential effect in both cases. An analysis of He-like triplets yields a range of coronal electron densities ~1010–1013 cm-3. Since
