A method and apparatus for detailed accounting of packet data are disclosed. According to one embodiment of the present invention, on receiving a duplicated HTTP request from a packet duplication apparatus, a billing apparatus extracts an access address to generate a first hash value. Then, on receiving a converted HTTP response from the packet duplication apparatus, the billing apparatus extracts a second hash value from the duplicated HTTP response to compare with the first hash value. If the first hash value and the second hash value are the same, the billing apparatus sets the HTTP REQUEST and the converted HTTP response as a transaction to generate billing data. Thus, the billing apparatus can generate accurate billing data.