Pulsed laser ablation in water under a high peak power density of 1.8 × 1011 W/cm2 using Q-switch mode and 1064 nm excitation was used to fabricate (H+,Al2+)-codoped Al2O3 nanocondensates having γ- and its derivative θ-type structure as characterized by electron microscopy and spectroscopy. The as-formed γ- and θ-Al2O3 nanocondensates are mainly 10 to 100 nm in size and have a significant internal compressive stress (>10 GPa) according to cell parameters and vibrational spectroscopy, due to a significant shock loading effect in water. The γ-Al2O3 nanocondensates are nearly spherical in shape but become cuboctahedra when grown to ca. 100 nm to exhibit more facets as a result of martensitic γ→θ transformation following the crystallographic relationship (3̅11̅)θ//(02̅2)γ; (02̅4̅)θ//(3̅11)γ. The formation of dense and (H+,Al2+)-codoped γ/θ-Al2O3 rather than aluminum hydrates sheds light on the favored phases of the Al2O3−H2O binary at high temperature and pressure conditions in natural dynamic settings. The nanocondensates thus formed have a much lower minimum band gap (5.2 eV) than bulk α-Al2O3 for potential optocatalytic applications.