How to say

How to say "weird" in Japanese?

okashii or hen

I believe okashii is a bit less negative sounding, so if you're just teasing someone you may want to use that.

Otherwise, I think that hen is a bit more serious sounding. It's kind of the difference between silly, and strange.

In what kind of context would you want to use the word?

If you want to say that something feels weird, in the sense of simply strange, not quite usual, you could use the word "hen" - which should be followed with a "-na" if you use it before a noun, and with a "-da" or "-desu" if it ends the sentence.
For example, if the weather keeps on changing unexpectedly, you could say:
- Kyou wa henna tenki desu. (Today it's a strange weather.)
- Kyou no tenki wa hen desu. (Today's weather is strange.)
("kyou" = today, "tenki" = weather)

If you want something like "spooky" or "creepy," you could say "kimi ga warui" (the atmosphere is eery).
- Kono koen wa kimi ga warui desu. (This park feels spooky.)
("kono koen" = this park)

A person who is "strange" - that may be "kawatte iru/imasu."

Kimochi warui

Thanx a mucho Rob and AK.
So, therefore, there is no general term for "weird" in nihonggo.
Weird= okashii
Hen
Warui

Usually i use the word misurashii to refer something weird. Now i have many options to use something weird hehehe. Cheer's to you all!!!

Dindo,
By "misurashii," do you mean "mezurashii"? That means strange in the sense of "rare" or "unusual," not really in the sense of "weird."

And be careful with "warui," because "warui" by itself means "bad." Only when put together in a phrase like:
- kimi ga warui
- kimochi warui.
...it means "feels strange/weird/creepy."

As "okashii" *can* also mean "funny," "wacko," as well, I'd say the most general term would be "hen," if you really mean "strange/weird." :)