Recently, we presented a family of in-plane chemically ordered transition metal borides of the general formula (M-2/3M-1/3")(2)AlB2. Here, we investigate incorporation of magnetic rare earth (RE) elements into this structure by synthesis and analysis of Mo4/3RE2/3AlB2, where RE = Ho, Tb, and Er. The crystal structure is verified by X-ray diffraction and scanning transmission electron microscopy, while the composition is derived from energy dispersive X-ray analysis. Through magnetization measurements, we also show that Mo4/3Ho2/3AlB2 orders antiferromagnetically below 9 K. We suggest that (M-2/3M-1/3")(2)AlB2 could potentially be a versatile platform for new magnetic materials, in 3D as well as 2D. GARPHICS IMPACT STATEMENT This paper introduces magnetic elements to i-MAB phases family with a formula of Mo4/3RE2/3AlB2 (RE = Ho, Er, and Tb), which opens a venue for further exploration of chemically ordered magnetic materials.