We study the total gravitating mass distribution in the central region of 23 clusters of galaxies with Chandra .
Using a new deprojection technique , we measure the temperature and gas density in the very central region of the clusters as a function of radius without assuming any particular models .
Under the assumptions of hydrostatic equilibrium and spherical symmetry , we obtain the deprojected mass profiles of these clusters .

The mass profiles are nicely scalable with a characteristic radius ( r _ { 200 } ) and mass ( M _ { 200 } ) on the large scale of r > 0.1 r _ { 200 } .
In contrast , the central ( r < 0.1 r _ { 200 } ) mass profiles have a large scatter even after the scaling .
The inner slope \alpha 
of the total mass density profile ( \rho ( r ) \propto r ^ { - \alpha } ) is derived from the slope of the integrated mass profile .
The values of the inner slope \alpha at the radius of 0.02 r _ { 200 } ( \alpha _ { 0 } ) span a wide range from 0 to 1.2 .
For 6 out of 20 clusters , \alpha _ { 0 } is lower than unity at a 90 % confidence level .
CDM simulations predict that the inner slope \alpha is in the range 1 < \alpha < 2 , which is inconsistent with our results .
We also found that the gas fraction near the center of a cluster has a negative correlation with \alpha _ { 0 } .
Our result suggests that the gas-rich clusters in the central region tend to have a flat core .