Opposition fighters captured the pilot, who ejected from the Sukhoi 22 jet near the strategically important opposition-held town of Khan Sheikhoun, the UK-based Syrian Observatory for Human Rights (SOHR) said.
Hayat Tahrir al-Sham (HTS), the jihadist group in control of Idlib, did not say how the jet was shot down, but SOHR said heavy machine guns were used.
Syrian state news is yet to confirm the incident.
Syrian regime forces made significant advances on Wednesday, capturing territory close to Khan Sheikhoun. The town is important for the regime to secure the main road connecting Damascus and Aleppo.
Idlib is the last bastion of opposition held Syria, where three million civilians are thought to reside. Many pro-opposition fighters fled to the embattled province to escape regime offensives elsewhere in the country.
The Russian-backed regime of Bashar al-Assad launched an offensive in April to retake the province after a buffer zone deal between Russia and opposition-backer Turkey failed to prevent skirmishes between jihadists and regime troops.
A brief ceasefire deal brokered by the Astana process guarantors, Russia, Turkey, and Iran, fell apart in early August.
