Customers will be greeted by information signs written in both English and the Cornish language.
The Cornish signs, translated by the Cornish Language Fellowship, were introduced after growing numbers of customers asked for information to be displayed in both languages.
The fellowship estimates there are around 400 fluent Cornish speakers in the county, with several thousand more speakers of conversational Cornish.
The bilingual signs, at Asda stores in Bodmin, Falmouth and St Austell, will feature phrases such as "Welcome" (Dynnargh), "Always happy to help" (Lowen pup-prys dhe weres), and "Information" (Derivadow).
Tutors from the language fellowship are at all three supermarkets to coach checkout operators in some Cornish phrases.
Dr Jon Mills from the Institute of Cornish Studies in Truro said the signs reflected an increasing interest in the Cornish language.
Strong community
He said: "I think the Cornish language revival is a growing trend in general and we are seeing more and more of this sort of thing.
"There is a very strong community feeling down in Cornwall and this is going to be a popular thing with many customers."
Cornish is a member of the Celtic family of languages which includes Irish, Scots, Welsh and Breton.
An Asda spokesman said it is the latest in bilingual signs for the company.
There are already signs in Welsh and English at its stores in Wales, and signs in Urdu and Punjabi at stores in Bradford.