We have been investigating electropolymerization of pyrrole in aqueous electrolyte solutions in acidic as well as in neutral conditions by in situ electrochemical quartz crystal oscillator method, where resonant frequency and resonant resistance can be monitored simultaneously with current-voltage measurements during electropolymerization of pyrrole. The properties of thin PPy films prepared on electrode surfaces depended strongly on the experimental variables of electrode potentials applied, solution pH, kinds and quantity of supporting electrolytes, added chemicals, and the mode of electrochemical method employed. We are applying our experience gained on electropolymerization of pyrrole to immobilizing biomolecules onto electrode surfaces to develop a biosensor system. In this work, we wish to present the results on electrochemical monitoring on electropolymerization of pyrrole in the presence of DNA and albumin in different electrochemical conditions. Additionally we will summarize our investigations on the miniaturization of biomolecules/PPy composites by means of scanning tunneling microscopy.