The writer saw the coffers of his firm increase as royalties rolled in from his books on the hard-bitten Edinburgh detective.
New figures from John Rebus Limited, named in honour of his famous creation, show that it had total assets of £4.1 million.
The accounts, which have just been filed at Companies House, reveal Rankin, 61, has a property and investment portfolio worth almost £2.4 million.
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After paying off creditors the firm is valued at £3,784,687 in the accounts - up more than £500,000 up on the previous year's figure.
The accounts, which cover the period up until March 31 this year, also revealed Rankin continues to give away large chunks of his earnings to good causes.
In the last year he donated £400,000 to a charitable trust which he and wife Miranda Harvey set up 14 years ago to fund projects at home and abroad.
The trust has helped health, art and educational charities in the past with Rankin regularly handing over lump sum payments.
He has given more than £1 million of his company earnings to the trust over the last five years.
Rankin, of Edinburgh, set up John Rebus Limited in 2001 to channel his earnings from his books. The Fife-born writer is a director of the company along with his wife.
The Rebus series has sold more than 20 million books and accounts for an estimated 10 per cent of all crime book sales in the UK and has been translated into 26 languages.
The 23rd Rebus novel, called 'A Song For The Dark Times', was published last year.
A new television series featuring the detective is also being planned.
Gregory Burke, the playwright who wrote Black Watch, the much-lauded National Theatre of Scotland play, is working on the script for the new television version of Rankin's famous character.
Earlier this year, Rankin revealed he is considering writing a prequel Rebus novel featuring his famous character in the 1970s.
He recently completed an unfinished novel by the late Scottish author William McIlvanney about his famous detective Laidlaw set in 1970s Glasgow.