Pairojnoi Sor Siamchai (Thai: ไพโรจน์น้อย ส.สยามชัย), is a former Thai Muay Thai fighter. He was a Lumpinee stadium champion.

Pairojnoi is an orphan who grew up in the Chachoengsao province, in a temple known for taking care of homeless children. He started Muay Thai training at the age of 9, he had his first fights in the nearby temples.^[1]

In 1985 he was scouted by the Songchai promotion and began his ascension at Lumpinee stadium in the 105 lbs division where he became popular for his aggressive style. On August 30, 1988, Pairojnoi won the Lumpinee Stadium title left vacant by Hippy Singmanee against the former champion's brother Kompayak Singmanee.^[2]

Pairojnoi's fight against Pongsiri Por Ruamrudee on July 25, 1989, was the headline bout for a card that broke records at Lumpinee stadium with a 3 million baht gate and over 10,000 spectators.^[3] On November 4, his second fight against Pongsiri "Rambo" was elected "Fight of the Year" and became known as the fight of the century for Muay Thai.^[4]

After his career Pairojnoi became a trainer in various countries. He had a notable contribution to the growth of the Brazilian muay thai scene. He was working at the Kor Romsritong camp until its closure, he then joined the Sitsongpeenong before opening his own gym in Samut Sakhon.

In May 2022, Pairojnoi had emergency heart surgery after he collapsed. He recovered from the operation.^[5]

• Lumpinee Stadium
  • 1988 Lumpinee Stadium Fight of the Year (vs. Pongsiri Por Ruamrudee on November 4)
  • 1988 Lumpinee Stadium 105 lbs Champion