Multi-layer ceramic electronic component and mounting board

A multi-layer ceramic electronic component includes a ceramic body enclosing internal electrodes laminated in a first direction, wherein the ceramic body has a main surface having a flat face normal to the first direction, a first side surface having a flat face normal to a second direction orthogonal to the first direction, and a rounded ridge connecting the main surface and the first side surface to each other and curved in a convex shape; a maximum dimension of the ceramic body in the first direction is 120 μm or less; and the rounded ridge satisfies a condition of Rb/Ra>3.0, where Ra represents a dimension of the rounded ridge in the first direction and Rb represents a dimension of the rounded ridge in the second direction on a cross-sectional surface of the ceramic body taken along a virtual cut plane parallel to the first direction and the second direction.