我不同意。

Place it at the start of your sentence to be firm. You can also add a reason after it to be polite. For example, 我不同意，因为太贵了 (I don't agree because it's too expensive). If you want to sound softer, add 觉得 (feel). Saying 我觉得我不同意 makes it sound like a personal feeling. It is like adding a "soft filter" to your rejection.

Use it in business meetings to voice a different strategy. Use it with friends when picking a movie you hate. It works well in text messages when someone suggests a bad time to meet. It is perfect for debates or serious discussions. If a waiter suggests a dish you know you dislike, this works too. Just remember to keep your tone steady and calm.

Avoid using this with your boss or elders without a soft opening. In Chinese culture, being this direct can sometimes feel like a challenge. Don't use it for small social invitations like "Want some tea?" Instead, use 不用了 (No need). Using 我不同意 for a cup of tea sounds like you are starting a legal battle! Also, avoid it in very heated arguments unless you want to escalate things.

Chinese culture often values "saving face" and harmony. Because of this, many people avoid saying 我不同意 directly. They might say "Maybe next time" or "I'll think about it." However, modern China is becoming much more direct, especially in cities. Using this phrase shows you are confident and clear. It marks you as someone who knows their own mind.

If you want to be super polite, say 我不这么认为 (I don't think so). For a very casual vibe with best friends, try 我不赞成 (I don't approve). If you are feeling extra spicy and totally disagree, use 我完全不同意 (I completely disagree). To sound more professional, try 我有不同的看法 (I have a different view). Each variation changes the "temperature" of the conversation.