～際に
at the time of / on the occasion of
～際に（さいに）is a formal way to say “when” or “on the occasion of”. It is formed as Noun + の際に or Verb (dictionary or た-form) + 際に, and is typical of announcements, signs, and business language. In everyday conversation, とき is more natural.
1. Noun + の際に
The noun names the occasion: returning home, using a service, an emergency.
帰国の際にお土産を買った。
“I bought souvenirs when returning home.”
- 帰国（きこく）= returning to one's home country
- の際に（のさいに）= at the time of, when
- お土産（おみやげ）= souvenir
- を = object marker
- 買った（かった）= bought
2. Verb + 際に
With a verb, the clause before 際に describes the event, and the main clause says what to do at that point. This form is common in formal instructions.
ホテルを出る際に、鍵をフロントに返してください。
“When you leave the hotel, please return the key to the front desk.”
- ホテル = hotel
- を = object marker
- 出る（でる）= to leave
- 際に（さいに）= when, at the time of
- 鍵（かぎ）= key
- フロント = front desk
- 返してください（かえしてください）= please return
How to form it
Noun + の際に / Verb (dictionary or た-form) + 際に
- 帰国（きこく）= returning home → 帰国の際に（きこくのさいに）= when returning home
- 利用（りよう）= use → ご利用の際に（ごりようのさいに）= when using (polite)
- 出る（でる）= to leave → 出る際に（でるさいに）= when leaving
Key idea
Think of ～際に as the suit-and-tie version of とき: the same “when”, raised to a formal register for announcements, signs, and polite requests.
Other N2 grammar
Updated .