  The innermost stable circular orbit equation of a test particle is obtained
for an approximate Kerr-like spacetime with quadrupole moment. We derived the
effective potential for the radial coordinate by the Euler-Lagrange method.
This equation can be employed to measure the mass quadrupole by observational
means, because from this equation a quadratic polynomial for the quadrupole
moment can be found. As expected, the limiting cases of this equation are found
to be the known cases of Kerr and Schwarzschild.
