The explosive growth in the use of mobile and wireless devices demands an adequate level of security for such devices. The security level need to be strengthen not only in device, but also in mobile application installed in the devices. This paper presents design in developing secure files transfer mobile application using digital signature technology; Elliptic Curve Digital Signature Algorithm. The developed mobile application consist of 8 main modules, including two modules that apply ECDSA algorithm; sign and send module. The developed mobile application not only secure the transferred file using digital signature, it also provide signature pad for user to enable user to use electronic signature for document