The grammar is very similar, the sound of many words are also similar. Basically, a lot of words in both languages came from the chinese words, they've got the similar root. I reckon Korean is easier to write (when we think of the fact the Chinese letters(Kanji) are used in Japanese), and Japanese is easier to pronounce. it's simpler.

As people have already gave good answers above, let me just answer literally: Japanese and Korean are different, in what ways? -Korean mainly uses hangul to write, while Japanese uses hiragana, katakana and kanji even though they both have a lot of Chinese-originated vocab. -One Japanese kanji has several different readings; one Korean hanja usually has only one reading. -When writing a sentence, you need to put spaces at certain places in Korean. In Japanese, no. -Korean sound system has more vowels and consonants than Japanese one. -Usage of respect/humble expressions. Korean one is absolute, Japanese one is relative. I think these are the main differences :]]

They are different languages from each other - and from Chinese, as well, however, they both borrowed the Chinese characters (Hanja in Korean, Kanji in Japanese, but both languages has own writing systems, Korea's Hangul, and Japan's Hiragana and Katakana) and a lot of words from that language. Their grammar is similar (subject - object - verb word order etc., you can see more in the Wikipedia), but I think that Korean is a little bit harder to learn.

They are totally different languages ..........

Firstly, they have different writing systems. Whilst they both use Hanja (Korean) / Kanji (Japanese), which is derived from Chinese writing, they use their own writing systems more commonly. The Japanese have hirigana (the first alphabet children learn, and less formal than katakana) and katakana (which has a more angular shape in contrast to the flowing shape of hirigana), and the Koreans have Hangul. Whilst I don't speak or write either language, I can easily distinguish them from each other at once. They now also have romanisation (called romanji in Japan) but it's only reserved for foreign words only. Japanese has been classified as a Japonic language, and I'm uncertain about the origins of Korean but I have heard people say that it is an isolate, possibly related to Altaic languages. If I concentrate very hard and if the speakers are speaking slowly, I may be able to differentiate, but they may be closer or further related than I think because I don't really speak either language.