Herein, we report the synthesis and third-order nonlinear optical (NLO) properties of a novel cage-based 2D metal-organic framework constructed from Ti₄L₆ (L^4-=embonate) cage combined with Mg²⁺ and tris[4-(1H-imidazol-1-yl)phenyl]amine (tipa) ligand, whose molecular formula is (Me₂CH₂)₂[Mg₃(Ti₄L₆)(tipa)(H₂O)₁₂] (PTC-378). The Ti₄L₆ tetrahedral cages serve as robust building units, while the Mg²⁺ ions and tipa ligands provide structural stability and tunable optical properties. The resulting PTC-378 film exhibited intriguing third-order NLO property, which was systematically investigated using Z-scan techniques. Our results demonstrate that the synergistic interaction between Ti₄L₆ cages and π-conjugated ligands significantly enhances the NLO performance of the materials.