The present invention relates to novel hydroxy and polyhydroxy derivatives of coumarin fused with dialdehydes and aldehyde acids of the general formulae I, II, III and IV: ##STR1## wherein R.sup.1 =R.sup.2 =4-hydroxycoumarin; R.sup.1 =R.sup.2 =4,7-dihydroxycoumarin; R.sup.1 =R.sup.2 =4,5,7-trihydroxycoumarin; R.sup.1 =4-hydroxycoumarin, R.sup.2 =--CH(OH)CH.sub.3. An object of the invention are also processes for the preparation of hydroxy and polyhydroxy derivatives of coumarin fused with dialdehydes and aldehyde acids, and the antiviral action thereof. Novel hydroxy and polyhydroxy derivatives of coumarin according to the present invention exhibit antiviral action against HIV-1 virus.