The RJD, however, termed it as the BJP leader's "agenda" of tarnishing the image of RJD president Lalu Prasad and his family.
Mr Modi, who holds the finance portfolio in the Nitish Kumar cabinet, alleged liquor manufacturer Amit Katyal gifted Tejashwi a car worth Rs 9.5 lakh, and extended loans to him and his brother Tej Pratap which were later written off.
He claimed it was done a quid pro quo to allow Amit and Rajesh Katyal to set up a liquor factory at Bihta in Patna district in 2003-04 when Rabri Devi was the chief minister.
Mr Modi claimed Tejashwi resigned as a director of AB Exports Pvt. Ltd. in November 2015 after becoming the deputy chief minister but signed cheques to some firms even in February 2016 in violation of norms.
On April 22, Mr Modi had alleged that the entire shares of AB Exports, directorship and properties were transferred to the family of Lalu Prasad.
Mr Modi said he was levelling charges against Tejashwi on the basis of an order passed by the income tax department to attach properties belonging to him and his sister Misa Bharti, a Rajya Sabha member, in Patna and New Delhi.
"The central government has taken several steps such as demonetisation, enforcement of Benami Transaction Act and GST to check corruption and black money but those who were hit hard by these decisions are opposing it," he said.
Reacting to Modi's allegations, RJD spokesman and MLA Shakti Singh Yadav said the BJP leader cannot "fix conditions for taking loans".
"It was a decision of a particular individual whether to take back the loan he gave to somebody or write it off. I don't think there is anything wrong about it. Sushil Modi has only one agenda...that to denigrate Lalu Prasad's family," he said.