Novel N'-4-(2-naphthyloxy)phenyl-N-methylurea derivatives of the formula: ##STR1## wherein X is a hydrogen atom, a halogen atom or a trifluoromethyl group and R is a methyl or methoxy group having a herbicidal activity, particularly effective in exterminating weeds in the cultivation of soybean and gramineous crops such as wheat and barley, and/or having a fungicidal activity especially effective in controlling the rust of wheat and barley.