Hydrogen sulphide (H₂S) is a toxic substance that causes acute and fatal poisoning when exposed to mammals. Many workers in the agricultural, petroleum, and sewage treatment industries are affected by H₂S poisoning yearly. The mechanism of H₂S toxicity is via inhibition of cytochrome c oxidase located in the complex IV of mitochondria, similar to cyanide poisoning. Since there is no approved and promising treatment for H₂S poisoning, sodium nitrite (NaNO₂), a cyanide antidote, is empirically used to treat patients suffering from H₂S toxicity in clinical situations. NaNO₂ oxidises haemoglobin (Hb) in red blood cells, and cyanide subsequently binds to the oxidised Hb (methaemoglobin: metHb) with high affinity. MetHb has been previously reported to inherently bind H₂S with high affinity and form sulphide-metHb, suggesting that metHb itself can serve as a detoxifying agent for H₂S toxicity. However, naked metHb has poor blood retention properties and induces severe renal toxicity.This study shows that liposome-encapsulated methaemoglobin (metHb-V), nanosized biomimetic red blood cells, exhibit superior H₂S detoxifying efficacy with no adverse effects. MetHb-V consists of concentrated metHb in its aqueous core and a lipid membrane resembling the red blood cell membrane, which provides favourable characteristics as an H₂S scavenger through high-affinity binding and membrane permeability for H₂S. Upon H₂S exposure, metHb-V showed cytoprotective effect with preserving sufficient cell viability and mitochondrial function in H9c2 cells. In lethal H₂S poisoning mice, metHb-V treatment dramatically improved mortality compared to saline treatment (negative-control) and NaNO₂ treatment. MetHb-V also possesses good pharmacokinetic properties with no renal toxicity. In conclusion, our findings show a novel drug development concept of biomimetic red blood cell preparations with promising H₂S detoxifying properties for pharmaceutical applications.