What it means
ばかりでなく means “not only A but also B.” It adds B as an additional fact, quality, or action after mentioning A. The phrase usually connects two parallel elements, and B is often followed by も. It can attach to nouns, plain-form verbs, i-adjectives, and na-adjectives with な. The construction itself does not change for politeness; politeness is normally shown in the predicate at the end of the sentence.
Usage note
ばかりでなく is somewhat more formal than だけでなく and is common in written explanations, presentations, and careful speech. The second part often uses も, but the exact predicate after it must match the meaning of the sentence.
How to use it
この図書館は本ばかりでなく、雑誌も多いです。
This library has not only books; magazines are plentiful too.
その計画は現実的なばかりでなく、環境にも優しいです。
That plan is not only realistic but also environmentally friendly.
この薬は安いばかりでなく、効果も高いです。
This medicine is not only inexpensive but also highly effective.
彼は日本語を話すばかりでなく、英語も教えます。
He not only speaks Japanese but also teaches English.
この図書館は本ばかりでなく、雑誌も多い。
This library has not only books; magazines are plentiful too.
その計画は現実的なばかりでなく、環境にも優しい。
That plan is not only realistic but also environmentally friendly.
この薬は安いばかりでなく、効果も高い。
This medicine is not only inexpensive but also highly effective.
彼は日本語を話すばかりでなく、英語も教える。
He not only speaks Japanese but also teaches English.