This is a problem that I am facing with my kid too .At first I used to firmly and strongly scold him .But that only got him crying so , I gave that up . I am wondering what to do !

I think 20 mos is early for time-outs to work effectively, but that doesn't mean you should stop. If that's the main discipline technique you plan to use, it's a good idea to start it now. With my son, we went through the same thing and I just kept at it. It can be hard because they don't understand, but once the communication improves after age 2, usually the hitting goes away too. I think all you can do at this young age is say NO firmly and remove her, briefly. But be consistent (which is hard sometimes as a mom). You may have to do this for many many months, but it is a phase that will pass. Hang in there!

I agree with the others. Using the same punishment every time and letting her know hitting is not tolerated are key. I also define the feeling - toddlers do not usually have the verbal skills to say what they are feeling. So along with his timeout I tell him, ' you are angry",(stressing angry and showing a mad face). I then continue with telling him that hitting hurts and making a sad face to go along with it. I tell him hitting is not allowed. I also try to note what frustrated him. I then use this in pretend play. I have his stuffed animals recreate the scene, with the ending being one animal goes to his room. In his room he hits his pillow and yells I'm so mad. It has taken us awhile but Junior is finally getting that he cannot hit. When he does it at the park, (or some other place), we leave immediately. He rarely hits in public now. I think it is important to help them learn an acceptable way to be angry. Hang in there - we have all been there. A lot more people are sympathetic than you think .

they understand at 20 months.
babies can read, add, subtract and communicate as young as 6 months old.
it needs to be explained to them how to express the anger properly and how to resolve the conflict.
saying the word "no" is limiting the childs developmental growth. the proper techniques suggest using redirection instead of "no". it is much easier for parents to just say the word "no" than to think about how to redirect or even give the child empathy. there is no such thing as terrible 2's or 3's- it is the parent that is to blame for the childs behavior.