  Fine structure in the $\alpha$ decay of $^{223}$U was observed in the
fusion-evaporation reaction $^{187}$Re($^{40}$Ar, p3n) by using fast digital
pulse processing technique. Two $\alpha$-decay branches of $^{223}$U feeding
the ground state and 244 keV excited state of $^{219}$Th were identified by
establishing the decay chain $^{223}$U $\xrightarrow{\alpha_{1}}$ $^{219}$Th
$\xrightarrow{\alpha_{2}}$ $^{215}$Ra $\xrightarrow{\alpha_{3}}$ $^{211}$Rn.
The $\alpha$-particle energy for the ground-state to ground-state transition of
$^{223}$U was determined to be 8993(17) keV, 213 keV higher than the previous
value, the half-life was updated to be 62$^{+14}_{-10}$ $\mu$s. Evolution of
nuclear structure for $N$ = 131 even-$Z$ isotones from Po to U was discussed in
the frameworks of nuclear mass and reduced $\alpha$-decay width, a weakening
octupole deformation in the ground state of $^{223}$U relative to its lighter
isotones $^{219}$Ra and $^{221}$Th was suggested.
