The Action Committee at St Aubin on the Hill church is appealing for donations to help pay for a new roof, as the current one is in danger of collapsing.
A JustGiving page has been set up to raise £100,000, because the 130-year-old nails and battens holding the tiles in place have rotted away.
It's estimated that as much as £500,000 will be needed for the project.
Work is due to start in September, as the endangered grey long-eared bats are breeding on the site until then.
A coffee morning ad bric-a-brac sale is taking place at the church at the end of this month, with an auction also planned in late May.
"We will have to have full scaffolding over the whole church and it's all quite a kerfuffle, so the congregation is trying to raise anything that is over the price we're expecting so we've got a lot of work to do.
(£500,000) is not the sort of thing that we could possibly range as a congregation per se, but we've got to raise some of it so we'll do it in our own little way. It's a minor nightmare, but it's such a beautiful church." - Denise Waller, Lay Minister.
The church is also used as a community space for people to visit.
Mrs. Waller says they want to do all they can to protect what she calls 'such a beautiful church'.
"It would be such a pity to lose the church. If the roof comes down, we've simply got to put it back up again.
To lose all this beauty would be such a shame and the island, I feel, would be poorer without it."
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