Naphthalene derivative of the formula [I]: ##STR1## wherein R.sup.1 and R.sup.2 are the same or different and are hydrogen atom, hydroxy group, cyclo-lower alkyloxy group, substituted or unsubstituted lower alkoxy group, or both combine each other to form lower alkylenedioxy group, R.sup.3 is substituted or unsubstituted nitrogen-containing 6-membered heterocyclic group, and groups of the formulae: --OR.sup.4 and --OR.sup.5 are the same or different and are protected or unprotected hydroxy group, processes for preparing thereof, and synthetic intermediates therefor, these compounds have excellent bronchodilating activity, and are useful in the prophylaxis and treatment of asthma.