The present invention relates to spiro 1,2,4-trioxanes of general formula 4. This invention more particularly relates to a process for the preparation of a series of spiro 1,2,4-trioxanes. Wherein, Ar represents aryl groups such as phenyl, 4-biphenyl, 4-chlorophenyl, 4-methoxyphenyl, 4-methylphenyl, 4-cyclohexylphenyl, 1-naphthyl, 2-naphthyl and the like and R represents hydrogen or the alkyl group such as methyl, ethyl and the like. Several of these compounds show high order of antimalarial activity against multidrug-resistant malaria in mice and thus hold promise as antimalarial agents against multidrug-resistant malaria.