  We present a photometric study of the Andromeda XVIII dwarf spheroidal galaxy
associated with M31, and situated well outside of the virial radius of the M31
halo. The galaxy was resolved into stars with Hubble Space Telescope/Advanced
Camera for Surveys revealing the old red giant branch and red clump. With the
new observational data we determined the Andromeda XVIII distance to be D =
1.33+-0.08 Mpc using the tip of red giant branch method. Thus, the dwarf is
situated at the distance of 579 kpc from M31. We model the star formation
history of Andromeda XVIII from the stellar photometry and Padova theoretical
stellar isochrones. An ancient burst of star formation occurred 12-14 Gyr ago.
There is no sign of recent/ongoing star formation in the last 1.5 Gyr. The mass
fractions of the ancient and intermediate age stars are 34 and 66 per cent,
respectively, and the total stellar mass is 4.2x10^6 Msun. It is probable that
the galaxy has not experienced an interaction with M31 in the past. We also
discuss star formation processes of dSphs KKR 25, KKs 03, as well as dTr KK
258. Their star formation histories were uniformly measured by us from HST/ACS
observations. All the galaxies are situated well beyond the Local Group and the
two dSphs KKR 25 and KKs 03 are extremely isolated. Evidently, the evolution of
these objects has proceeded without influence of neighbours.
