Recently,the theoretically predicted lanthanum superhydride,LaH10±δ,with a clathrate-like structure was successfully synthesized and found to exhibit a record high superconducting transition temperature Tc ≈ 250 K at～170GPa,opening a new route for room-temperature superconductivity.However,since in situ experiments at megabar pressures are very challenging,few groups have reported the ～250 K superconducting transition in LaH10±δ.Here,we establish a simpler sample-loading procedure that allows a relatively large sample size for synthesis and a standard four-probe configuration for resistance measurements.Following this procedure,we successfully synthesized LaH10±δ with dimensions up to 10 × 20 μm2 by laser heating a thin La flake and ammonia borane at ～1700 K in a symmetric diamond anvil cell under the pressure of 165 GPa.The superconducting transition at Tc ≈ 250 K was confirmed through resistance measurements under various magnetic fields.Our method will facilitate explorations of near-room-temperature superconductors among metal superhydrides.