Daunomycin, an anthracycline antibiotic, has been found to inhibit virus multiplication and shows considerable activity against tumors. Its activity may be varied by conformational changes of daunomycin. The conformational changes are come from the pucker of D-ring and variation of environments. We have carried out conformational analyses by using empirical potential function. We found that when daunomycin is hydrated or bound to $Mg^{2+}$ ion, the minimum conformer of each state is altered from ${alpha}$ conformer to ${eta}$ conformer through the pathway having four local minima. Our calculated results are in good agreements with those of X-ray crystallography and biological experiments, in which metal ion inhibits the binding of daunomycin to DNA.