  We present surface photometry and stellar kinematics of NGC 4431, a barred
dwarf galaxy in the Virgo cluster undergoing a tidal interaction with one of
its neighbors, NGC 4436. We measured its bar pattern speed using the
Tremaine-Weinberg method, and derived the ratio of the corotation radius, D_L,
to the bar semi-major axis, a_B. We found D_L/a_B=0.6^{+1.2}_{-0.4} at 99%
confidence level. Albeit with large uncertainty, the probability that the bar
ends close to its corotation radius (i.e., 1.0 \leq D_L/a_B \leq 1.4) is about
twice as likely as that the bar is much shorter than corotation radius (i.e.,
D_L/a_B > 1.4).
