Papers filed in Anchorage, Alaska, on Friday identified the couple by initials – but birth and wedding dates match those of the Palins.
The paperwork, reportedly filed by Todd Palin, cited an “incompatibility of temperament” as the reason for divorce.
The Palins, both 55, married in 1988 and have five children together.
The documents mention “an incompatibility of temperament between the parties such that they find it impossible to live together as husband and wife”.
They include the initials rather than full names of the two parties – SLP for Sarah Louise Palin and TMP for Todd Mitchell Palin – but identify the couple’s marriage date and the birth date of their only child who is a minor, Trig Palin.
They are asking for joint custody of the child, according to the papers.
The paperwork was submitted on 6 September, eight days after the couple’s 31st wedding anniversary.