We consider the extended Higgs models, in which one of the isospin doublet scalar fields carries the hypercharge Y=3/2. Such a doublet field Φ_3/2 is composed of a doubly charged scalar boson as well as a singly charged one. We first discuss a simple model with Φ_3/2 (Model I), and study its collider phenomenology at the LHC. We then consider a new model for radiatively generating neutrino masses with a dark matter candidate (Model II), in which Φ_3/2 and an extra Y=1/2 doublet as well as

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... -like singlet fermions carry the odd quantum number for an unbroken discrete Z_2 symmetry. We also discuss the neutrino mass model (Model III), in which the exact Z_2 parity in Model II is softly broken. It is found that the doubly charged scalar bosons in these models show different phenomenological aspects from those which appear in models with a Y=2 isospin singlet field or a Y=1 triplet one. They could be clearly distinguished at the LHC.