The searches were conducted on November 7 "in the case of a group of trusts that are running educational institutions in and around Chennai for the past 30 years", policy-making body for the tax department CBDT said.
While the Board did not mention where the raids were conducted, official sources confirmed it to be the Jeppiaar group.
The group runs a number of engineering, polytechnic, dental and nursing colleges, hospitals and schools, the CBDT said.
It has interests in other sectors like fishing harbour, cement, milk, bottled water and iron and steel, it said.
"Cash of about Rs 5 crore and jewellery of more than about Rs 3 crore were seized in the said action. The preliminary estimate of the undisclosed income of the group detected so far is more than Rs 350 crore," the CBDT said.
It said the search proceedings have been temporarily concluded and investigations into the findings are in progress.
The tax department acted as there were reports of the group accepting fee and donations in cash, which "were largely unaccounted" and of the funds of the trust being diverted to other sister concerns, it said.
During the search proceedings, it said, evidence of "suppression" of fee receipts was found.
In addition, a group entity has adopted the modus operandi of showing the actual fees received as "advance fee collection" in the liability side of the balance sheet and advancing the said amounts as payments, mainly, to its sister concerns against certain expenses/purchases, which were found to be inflated and bogus, the CBDT claimed.
"Thus, the money of the trusts is found to be diverted outside for the objects outside the scope of trust (as defined in the I-T Act)," it said.
Evidence have been found of "unexplained cash debits", un-recorded cash expenditure, suppression of sale receipts in fishing harbour, loans advanced in cash and non-disclosure of income from sale of property among others.