It is shown that all immersed closed, locally convex curves with total curvature of
and
-fold rotational
symmetry () finally
evolve into
-fold
circles under the length-preserving curvature flow. Sufficient conditions for the
occurrence of the finite-time singularities in the flow are also established. As a
byproduct, an isoperimetric inequality for rotationally symmetric, locally convex
curves is proved via the flow method.