The control of the tip vortex, generated by a rectangular NACA 0012 wing, via tip-mounted half-delta wings (HDWs), of different slendernesses Λ, root chords cr, and deflections δ, was investigated experimentally at Re = 2.45 × 105. The results show that regardless of Λ, cr, and δ, the addition of HDWs consistently led to a diffused tip vortex. The degree of diffusion was, however, found to increase with decreasing Λ and cr. HDWs with cr ≤ 50% of the baseline-wing chord c caused a rapid diffusion of vorticity and rendered a weak circulation flowlike tip vortex, suggesting an enhanced wake-vortex decay and alleviation. The cr = 0.5c HDW also produced an improved lift-to-drag ratio. A unique double-vortex pattern also exhibited downstream of the cr ≤ 50%c HDW wings. The interaction and merging of the double vortex were expedited by upward HDW deflection.