  We report the critical current density Jc in KxFe2-ySe2-zSz crystals. The Jc
can be enhanced significantly with optimal S doping (z=0.99). For
K0.70(7)Fe1.55(7)Se1.01(2)S0.99(2), the weak fishtail effect is found for H||c.
The normalized vortex pinning forces follow the scaling law with a maximum
position at 0.41 of the reduced magnetic field. These results demonstrate that
the small size normal point defects dominate the vortex pinning mechanism.
