A smart portable stethoscope is formed of a smart mobile device and a casing assembly for the mobile device. The casing assembly comprises a casing member, a diaphragm holder member configured to securely and effectively retain a diaphragm, and a vibrator-transducer member. The casing member includes a diaphragm connector part configured to securely fasten the diaphragm holder member to the casing member. The vibrator-transducer member is configured to be securely fastened to diaphragm holder member or casing member in such a manner that its vibrator is disposed to interconnect with the diaphragm and effectively duplicate vibrations captured by the diaphragm so as to deliver medical-grade auscultation electronic signal based on the duplicated vibrations to the mobile device through an audio plug plugged into a microphone jack thereof.