Lead dioxide, also lead(IV) oxide or plumbic oxide, is an oxide of lead (PbO₂) in oxidation state +4. It is an odorless dark-brown crystalline powder which is nearly insoluble in water. It exists in two crystalline forms. The alpha phase has orthorhombic symmetry; it has been first synthesized in 1941 and identified in nature as a rare mineral scrutinyite in 1988. On the contrary, the more prevailing, tetragonal beta phase was first identified as the mineral plattnerite around 1845 and later produced synthetically. Lead dioxide is a strong oxidizing agent which is used in the manufacture of matches, pyrotechnics, dyes and other chemicals. It also has several important applications in electrochemistry, in particular as a component of lead acid batteries.

Lead dioxide is an odorless dark-brown crystalline powder which is nearly insoluble in water. It has two major polymorphs, alpha and beta, which occur naturally as rare minerals scrutinyite and plattnerite, respectively. Whereas the beta form was known already in 1845, α-PbO₂ was first synthesized in 1941 and identified as a mineral only in 1988. The alpha form has orthorhombic symmetry, space group Pbcn (No. 60), Pearson symbol oP12, lattice constants a = 0.497 nm, b = 0.596 nm, c = 0.544 nm, Z = 4 (four formula units per unit cell). The symmetry of the beta form is tetragonal, space group P4₂/mnm (No. 136), Pearson symbol tP6, lattice constants a = 0.491 nm, c = 0.3385 nm, Z = 2.