You must declare that you are using this feat before you make your attack roll (thus, a failed attack roll ruins the attempt). Stunning Fist forces a foe damaged by your unarmed attack to make a Fortitude saving throw (DC 10 + 1/2 your character level + your Wis modifier), in addition to dealing damage normally. A defender who fails this saving throw is stunned for 1 round (until just before your next turn). A stunned character drops everything held, can't take actions, loses any Dexterity bonus to AC, and takes a –2 penalty to AC. You may attempt a stunning attack once per day for every four levels you have attained (but see Special), and no more than once per round. Constructs, oozes, plants, undead, incorporeal creatures, and creatures immune to critical hits cannot be stunned.

Stunning Fist

Combat

A monk receives Stunning Fist as a bonus feat at 1st level, even if he does not meet the prerequisites. A monk may attempt a stunning attack a number of times per day equal to his monk level, plus one more time per day for every four levels he has in classes other than monk.