Tributyltin oxide (TBTO) is an organotin compound chiefly used as a biocide (fungicide and molluscicide), especially a wood preservative.

It is poorly soluble in water (20 ppm) but highly soluble in organic solvents.

Historically, tributyltin oxide's biggest application was as a marine anti-biofouling agent.

Concerns over toxicity of these compounds have led to a worldwide ban by the International Maritime Organization.

[2] It is now considered a severe marine pollutant and a Substance of Very High Concern by the EU.