Answer by
Chrissie (266)
You can say "watashi wa kanashii desu" or just "kanashii desu". "Kanashii" just means "sad". If you want to say that something has made you sad, that would be "kanashiku natta" / "kanashiku narimashita" ([I] have become sad), or "[X] ga watashi ni kanashinaseta" / "[X] ga watashi ni kanashinasemashita" (X has made me sad).