Do you believe in extra dimensional universe?and why?

"Believe in" is not the term I would use in this context, as it implies something that is felt, rather than being credible on it's own terms. However, if you are referring to the five string theories or the development from those of M Theory, it has to be said that the latter is the best explanation so far for several anomalies evident in the Universe, such as the apparent weakness of gravity. Each of the original five string theories requires 10 dimensions in which to work, but by adding one more, making eleven, M Theory pops up in the maths all by itself. So yes, in that sense, I "believe" there are more than the three spatial and one temporal dimension we see in every day life.