Dirac band crossing and topological surface states are crucial for verifying and exploring topological materials. As an isostructural heavy fermion Ce-115 compound, ${\mathrm{LaRhIn}}_5$ exhibits exotic transport behavior potentially arising from linear crossing, although experimental evidence is still lacking. Here, by using angle-resolved photoemission spectroscopy and density functional theory calculations, we reveal the existence of a three-dimensional Dirac point protected by $C_4$ symmetry in ${\mathrm{LaRhIn}}_5$. Moreover, surface states merging into the bulk Dirac bands are also observed, akin to most topological semimetals. However, a comprehensive calculation of the system's topological index indicates a trivial $Z_2$ invariant, which excludes the existence of strong topological nature in the system. The existence of the three-dimensional Dirac fermion in ${\mathrm{LaRhIn}}_5$ might contribute to the understanding of the electronic structure in ${\mathrm{LaRhIn}}_5$ and shed light on the topological nature of the isostructural Ce-115 system.

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• Electronic structure
• Dirac semimetal
• Single crystal materials
• Surfaces
• Angle-resolved photoemission spectroscopy
• Density functional theory
• First-principles calculations