R. Mordecai Zev b. Jacob Meshullam Ornstein (1790-1837) was the son of the Yeshu'ot Ya'akov, who raised and educated him. He refused to accept a rabbinical post for many years. He finally accepted an invitation from the Przemysl community to become its rabbi, but died before he was able to take up his post. His responsa and novellae are to be found in his father's Yeshu'ot Ya'akov. R. Mordecai Zev predeceased his father.