One of the accused, Hassan Boukri, was cleared of all charges by the court in Amiens, northern France.
But four others, including local union leader Mikaël Wamen, were found guilty of kidnapping but not guilty of another charge of "gang assault".
They were given 12-month suspended sentences.
Three of the defendants were judged not guilty of kidnapping but guilty of "gang assault", two receiving three-month suspended sentences and one two months suspended.
Bossnapping during jobs fight
Five of the eight, including Wamen, were representatives of the CGT trade union, which backed their fight against the closure of tyre company's factory in Amiens with the loss of 1,143 jobs.
During an occupation of the plant in January 2014 workers kept its human resources chief and production manager inside the company's offices for about 30 hours, leading to the court case.
Although Goodyear and the managers dropped their cases, public prosecutors pressed on, claiming the two bosses had been insulted and humiliated and calling for 24-month suspended sentences at the workers' first trial in October.
Sentences sparked protests
The court shocked trade unionists by giving them nine months in jail plus 15 months suspended, leading the CGT to accuse the court of the "criminalisation of union activity".
There were strikes and demonstrations against the sentences in several parts of the country and 171,000 people signed an online petition for the charges to be dropped.
Supporters rallied outside the court in Amiens on Wednesday.
Wamen, who became a nationally known figure during the jobs fight, called for a "legal and not a political decision" on Wednesday before the appeal was heard, a call echoed by defence lawyer Fiodor Rilov in court when he called for acquittal for all eight defendants.