A gene encoding streptodornase(sdc) from Streptococcus equisimilis H46A was expressed in S. equisimilis H64H sdc under the control of the streptokinase gene promoter. Secretion of the streptodornase was directed by the signal sequences of streptokinase or streptodornase. The expressed streptodornase activity from S. equisimilis H46A sdc transformant with streptokinase promoter - streptodornase coding sequence fusion vector was 2.3 fold higher than that from wild type. Construct of signal sequence region replaced by streptokinase ones was similarly expressed as a wild type. But constructs of skc or lrp core regions of streptokinase promoter streptodornase fusion were similarly expressed as in sdc mutant. In conclusion, improved expression of streptodornase by use of streptokinase promoter required the full length of promoter.