A Free Church of Scotland study panel examined the issues surrounding marriage, divorce and remarriage.
The study comes as responses to the Scottish Government's consultation on gay marriage are evaluated.
Referring to same-sex couples, the Free Church report said: "By getting the right to marry, they get more respectability for bringing up children (they already have the right to foster and adopt).
"This is a huge social experiment in which the guinea pigs are children. That is not fair or just to children and does not safeguard their rights. It is really being pushed in a doctrinaire way by the gay lobby without any consideration of the harm that it will do."
The church said that civil partnerships already give same-sex couples the same legal rights as marriage, and therefore there is no need to introduce same-sex marriage.