How do you say "I lost my key" in Japanese?

Quick use

Use かぎをなくしました (kagi o nakushimashita) when you lost your key and need help from a landlord, building staff, or key service.

Chunk or pattern

• Reusable pattern: 〜 を / なくしました
• Use it when you lost an important item.
• Good swaps here: かぎ, カード, にもつ.

Core words

• かぎ: key.
• なくしました: lost.

Helper words and endings

• を: marks the thing you lost.
• ました: makes it past, like “lost.”

Form contrast

• なくします (nakushimasu): lose / will lose
• なくしました (nakushimashita): lost

For this page, the past form matters because the problem has already happened.

Practical note

If this is urgent, say this first. Then add where you are, such as the building entrance or your room number.