From our database: read here we can mention a few reasons why Pluto is not considered a planet anymore:
Pluto is not big enough as other objects that orbit our sun; Pluto has not either cleared its specific orbit of smaller objects.
Pluto has not sufficient gravity to make it round-ish.
According to the International Astronomical Union (IAU), Pluto does not fit on the new definition of a planet; in terms of its composition and its orbit, Pluto is unlike the other planets.

For now, there are three official classes of objects in our Solar System: planets, dwarf planets, and small solar system bodies. Planets include the eight traditional planets from Mercury to Neptune, but no longer Pluto. Pluto is joined amongst the dwarf planets.