The synthesis and spectral characterization of the (𝐸)-3-benzylideneindolin-2-one is reported. The compound crystallized in the monoclinic system with space group P 2₁/𝑛 with cell coordinates 𝑎 = 3.9849 (2) Å, 𝑏 = 22.2236 (9) Å, 𝑐 = 12.2501 (5) Å, 𝛽 = 95.0535 (12)° , 𝑉 =1080.64 (8) Å 3 , and 𝑍 = 4. In the crystal, molecules are packed in chains formed via weak intermolecular C13–H13A· · · O1 and N1-H1N1. . .O1 hydrogen bonding. The relative stabilities of the two tautomeric isomers of 3 are calculated by DFT/B3LYP method using 6-311G(d,p) basis set in gas phase and in solution. The quantum chemical calculations, NMR studies and the XRD analyses showed that the keto form T0 is the only form that could exist in gas, solution and solid phases respectively. The calculated geometric parameters of the dimer molecule showed better agreement with the XRD data than those obtained for single isolated molecule. This shed light on the effect of intermolecular interactions on the calculated geometric parameters. MEP study showed that, the O-atom and the NH proton are the most reactive H-acceptor and H-donor sites, respectively. The N-H...O H-bonding interactions increased the negative charge at the O-atoms and the positive charge of the NH protons compared to the monomer unit.