Abstract: Traditional melamine resin retanning agents are limited by the excessive release of formaldehyde, which constrains their applicability in the leather tanning industry. To address this issue, a kind of novel formaldehyde-free melamine resin retanning agent TSP was synthesized by employing cyanuric chloride (TCT) as crosslinking agents, and subsequently reacting with sodium sulfanilate (SE) and hydrolyzed collagen (CH) through a controlled stepwise temperature process. Infrared spectroscopy and nuclear magnetic resonance analyses confirmed the successful cross-linking among SE, CH and TCT. The particle size of TSP1 was measured at 387.32 nm, with an isoelectric point determined to be 4.29, indicating its amphoteric nature. Application evaluation experiments revealed that the absorption rate of TSP1 was 73.23%. After retanned with TSP1, the absorption rate of fatliquoring agent by chrome-tanned leather increased to 89.36%. The thickening rate of leather retanned with TSP reached to 37.50%, and showing advantages in fullness, fiber dispersion and other physical properties. Importantly, TSP demonstrated excellent storage stability and did not release free formaldehyde, highlighting its potential for widespread application in the leather industry.