The ATHEX index was losing 3.96 percent and stood at 633.78 points, with Greek bank suffering for a third straight day.
The bank index was down 21 percent and three of the main four lenders were near the maximum allowed drop of 30 percent.
Piraeus Bank and Alpha Bank were losing over 29 percent, Eurobank was over 26 percent down and National Bank was nearly 9.0 percent in the red.
The Athens market reopened on Monday five weeks after the government imposed capital controls to prevent a bank run and stave off financial collapse at the height of its standoff with EU-IMF creditors over a new bailout.
The Greek government and European Commission chief Jean-Claude Juncker have expressed hope that debt-crippled Greece and its creditors will reach a deal on a new rescue package in time for August 20, when it is due to pay the European Central Bank 3.4 billion euros ($3.71 billion.