  Using high-resolution HST/Wide Field Camera 3 F125W imaging from the
CANDELS-COSMOS field, we report the the structural and morphological properties
of Extremely Red Objects (EROs) at $z\sim1$. Based on the UVJ color criteria,
we separate EROs into two types: old passive galaxies (OGs) and dusty
star-forming galaxies (DGs). For a given stellar mass, we find that the mean
size of OGs (DGs) is smaller by a factor of $\sim2$ (1.5) than that of
present-day early-type (late-type) galaxies at rest-frame optical wavelength.
We derive the average effective radii of OGs and DGs, corresponding to
$2.09\pm1.13$ kpc and $3.27\pm1.14$ kpc, respectively. Generally, The DGs are
heterogeneous, with mixed features including bulges, disks, and irregular
structures, with relatively high $M_{\rm 20}$, small size and low $G$, while
OGs are elliptical-like compact morphologies with lower $M_{\rm 20}$, larger
size and higher $G$, indicating the more concentrated and symmetric spatial
extent of stellar population distribution in OGs than DGs. The findings imply
that OGs and DGs have different evolutionary processes, and the minor merger
scenario is the most likely mechanism for the structural properties of OGs.
However, the size evolution of DGs is possibly due to the secular evolution of
galaxies.
