When choosing your outfit for a first communion party, think clean and elegant. Guests are typically expected to dress as if they were attending any special religious celebration such as mass, a baptism, or Easter Sunday. You can't go wrong with a suit or simple frock. However, if you are unsure of the dress code, it's always safest to just ask the party host.
What “Sunday Best” Means
First Communions are an occasion to dress up. However, this doesn't mean wearing something flashy or provocative. The tone of this holy celebration is conservative. Churchgoers often call this kind of attire your "Sunday best" or "Sunday clothes."
For men, a suit or sport jacket with dress trousers and a tie will work just fine. Women should wear a dress or skirt with a hem that is right above the knee or longer. Children can echo the looks of their parents. Avoid going too casual with short and jeans. Women should avoid tank tops, spaghetti straps and deep necklines unless they are worn beneath a cardigan or blazer. Do not wear anything that is tight or short either.