Assistant accountant Beryl Rawlings added extra digits to cheques before paying them into her account.
The fraud against Manchester firm Elcometer went undetected for six years.
Elcometer provide inspection equipment for the coatings and concrete sector.
The Manchester Evening News said Rawlings tripled her £20,000 salary by stealing an average of £45,000 a year.
She was jailed for three years at Manchester Minshull Street Crown Court after pleading guilty to theft and fraud at an earlier hearing.
The fraud was discovered when Elcometer’s bank queried a payment of £8,430 into Rawling’s account which had been altered from an original payment of £30 to customs and excise.