tive seesaw models that they are directly testable at the collider experiments such as Large Hadron Collider (LHC) and the International Linear Collider (ILC). A general feature in radiative seesaw models is an extended Higgs sector, whose detail is strongly model dependent. The discovery of these extra Higgs bosons and detailed measure- ments of their properties at current and future collider experiments can give partial evidence for the radiative seesaw models. In the literature [8–14], phenomenology of these radiative seesaw models has already been studied extensively. Such previous works mainly discuss constraints on the flavor structure from the current data for such as neutrino physics and DM, and also study collider phenomenology of the Higgs sectors [15–17, 19–24]. Another common feature in radiative seesaw models is the Majorana nature. In order to induce tiny Majorana masses for left-handed neutrinos, we need to introduce its origin such as lepton number violating interactions in the scalar sector [2, 3] or right-handed neutrinos with TeV-scale Majorana masses [4–6]. When the future data would indicate an extended Higgs sector predicted by a specific radiative seesaw model, the direct detection of the Majorana property at collider experiments should be a fatal probe to identify the model. In this Letter, we study the phenomenology in TeV-scale radiative seesaw models, in particular, a possibility of detecting the Majorana nature at collider experiments. We mainly discuss three typical radiative seesaw models as reference models; the model by Zee and Babu where neutrino masses are generated at the two-loop level [3], that by Ma with one-loop neutrino mass generation [5], and that in Ref. [6] where neutrino masses are generated at the three-loop level. Typical parameter regions where the data can be satisfied have been already studied in each model in the literature. We here study collider phenomenology in such typical parameter regions in each model, and discuss the discrimination of these models by measuring the details of the Higgs sector and the Majorana nature at the LHC and the ILC. In the model proposed in Ref. [3] (we refer to as the Zee-Babu model), in addition to singly-charged singlet scalar bosons ω $^{±}$, doubly-charged singlet scalar fields k ±± are intro- II. RADIATIVE SEESAW MODELS A. The Zee-Babu model 3