This help topic is Open Game Content, and is licensed for public use under the terms of the Open Gaming License v1.0a .
Make a disarm attempt with the currently selected weapon. A defender gets a +4 bonus for 2-handed weapons – that is not automatically calculated.
The character and an adjacent target make opposed attack rolls with the their respective weapons. If the weapons are different sizes, the opponent with the larger weapon gets a bonus on the attack roll of +4 per difference in size category. If the target is using a weapon in two hands, he gets an additional +4 bonus. If the character beats the target, the target is disarmed. If a character attempted the disarm action unarmed, the character now has the weapon. Otherwise, it drops to the ground at the target's feet. If the character fails, then the target may make an attempt to disarm the character as an immediate, free action.
Note: A target wearing spiked gauntlets can't be relieved of the gauntlets by a disarm action. A target using a weapon attached to a locked gauntlet gets a +10 bonus to any disarm attempt made by an opponent.
This action substitutes for a melee attack, not an action. As melee attacks, it can be used once in an attack or charge action, one or more times in a full attack action, or even as an attack of opportunity.