The antipassive voice (abbreviated antip or ap) is a type of grammatical voice that either does not include the object or includes the object in an oblique case. This construction is similar to the passive voice, in that it decreases the verb's valency by one – the passive by deleting the agent and "promoting" the object to become the subject of the passive construction, the antipassive by deleting the object and "promoting" the agent to become the subject of the antipassive construction.

The antipassive voice is found in Basque, in Mayan, Salishan, Northeast Caucasian, Austronesian, and Australian languages, and also in some Amazonian languages (e.g. Cavineña, Kanamarí).

Antipassive voice predominantly occurs in ergative languages where the deletion of an object "promotes" the subject from ergative case to absolutive case. In certain accusative languages that have verbal agreement with both subject and object, the antipassive is usually formed by deletion of the object affix. Examples of accusative languages with this type of antipassive are Maasai, Comanche and Cahuilla. A number of direct–inverse languages also have the antipassive voice. Somewhat less conventionally, markers that reduce a verb's transitivity by syntactically eliminating objects or demoting them to oblique arguments in accusative languages such as Swedish, Russian or some Turkic languages have recently been described by many linguists as antipassive as well.

The antipassive voice is very rare in active–stative languages generally and in nominative–accusative languages that have only one-place or no verbal agreement. There are a few exceptions to this trend, such as Krongo and the Songhay language Koyraboro Senni, both of which rely on dedicated antipassive markers that are rare in the more typical type of language with an antipassive.

In the Mayan language Kʼicheʼ, the core arguments of a clause are unmarked for case, and are cross-referenced by person markers on the verb. Person marking follows an ergative–absolutive pattern. Non-core participants are expressed by prepositional phrases.

In the following transitive clause, the object "your mother" is the absolutive argument. It is unmarked for case and is not overtly cross-referenced, since the absolutive third person singular prefix is zero. The agent "you" is represented by the ergative second person singular prefix a-.

k-∅-a-yoq'

ASP-3SG.ABS-2SG.ERG-mock