Asked during a BBC radio interview whether the church could accept same-sex marriages, Archbishop of Canterbury George Carey responded, "No, I would say very firmly."
He insisted that marriage was a "relationship between a man and a woman," suggesting that other relationships were types of "friendship."
"People can have deep friendship, and call it friendship, but we don't have to muddy the waters in terms of calling it marriage," Carey said.
The church's stance, combined with its strong support of chastity out of wedlock, has frustrated some homosexual groups. When Carey led a service at a Methodist conference in the United States last year, about 100 pro-gay demonstrators briefly interrupted with chants of "extend the table!"
Separately, Carey signaled a more flexible church attitude toward remarrying divorcees.
A report on remarrying is to be produced and debated by the church later this year, the archbishop said, adding he hoped the exercise "will take us forward."
Currently, the Church of England leaves the decision to grant a remarriage to the parish priest.