We study the soft X-ray (0.1-2 keV) properties of a well-selected sample of 66 Narrow-
line Seyfert 1 (NLSy1) and 53 Broad-line Seyfert 1 (BLSy1) galaxies observed by
ROSAT in 0.1-2.0 keV energy band. A systematic homogeneous analysis is carried
out to estimate their soft X-ray photon index (Γ X ) and its correlations with other parameters of nuclear activities such as Eddington ratio (R Edd ≡ L bol /L Edd ), bolometric
luminosity (L bol ), black hole mass (M BH ) and the width of the broad component of Hβ
line (FWHM(Hβ)). In our analysis, we found (i) the existence of bimodality of the Γ X,
R Edd distributions among NLSy1 and BLSy1 galaxies, with a steeper Γ X for NLSy1
galaxies and (ii) a significant positive correlation between Γ X and R Edd for the sample of NLSy1 but non-significant for the sample of BLSy1. No significant correlation is
found for Γ X -M BH, Γ X -FWHM(Hβ), while a moderate Γ X -L bol relation is present for
the sample of NLSy1, though with a lower statistical significance than that between
Γ X and R Edd. The observed significant Γ X -R Edd correlation for our NLSy1 galaxies ap-
pears to be qualitatively similar to the luminous AGNs derived based on their hard
X-ray photon index, which is generally consistent with the theoretical prediction of
X-ray productions by a disc-corona system.