When will my baby understand “NO”?

Some infants begin to understand the meaning of the word "No" by the age of 6 months but they won't stop what they're doing until they are at least a year old. Actually, most babies react to the tone of our voices than the meaning of the word. So you can actually tell him "Yes" in a stern tone and he will get shocked. If you want your baby to not do something, distract him with something else or hold his hands and look him in the eye while repeating the word "No" firmly. It may take a few tries before it gets registered in his brain. http://www.babycenter.com/408_when-will-my-baby-understand-no_1368459.bc