Former Maris Stella High principal Anthony Tan Kim Hock, who was found guilty of embezzling $67,700 in April, was sentenced to five months' jail on Friday.
The 65-year-old who used school funds for a project to rebuild a three-storey private residence of his religious order, will be appealing against the conviction and sentence today, said defence lawyer Peter Low.
Tan faced 21 charges of criminal breach of trust between 2004 and 2009, but the prosecution proceeded on only one count involving $67,679.
Prosecution asked for a bail of $80,000 due to the length of the sentence. The bail amount was later reduced to $60,000.
Tan, who was the school's longest-serving principal and a strict disciplinarian, is credited with building its reputation for excellence in information technology, and introducing a range of outdoor adventure programmes to give boys a holistic education.
But it all went wrong after he used school funds for a project to rebuild Champagnat House, a private residence of the Marist Brothers.
The money paid for granite surfacing on walls, stained glass windows and kitchen appliances.
During the 11-day trial, Tan claimed he dipped into the funds out of "expedience", with the intention of paying the money back later.
But Judge Soh said this was directly contradicted by evidence that showed Tan had enough money to pay for the renovations himself. Using his personal bank account would have been "far more straightforward and convenient", he added.
The judge said Tan, who was principal between 1984 and 2009, failed to mention points in his statements to the Commercial Affairs Department that were later introduced as evidence at the trial.