Objective. Gelatin USP is a mixture of high molecular weight protein homologues derived by partial hydrolysis of animal collagen. The objective of the study was to measure the kinetics of the dynamic equilibrium existing between different molecular weight fractions of gelatin in aqueous solution. Methods. A 1% w/v aqueous solution of B225 gelatin was applied to a Sephadex G200 gel. The collected fractions and an unfractionated gelatin control were analyzed using size exclusion HPLC. The fractions and control were then incubated at ambient temperature in the presence of 1mM phenylmethylsulfonyl fluoride (PMSF) as a protease inhibitor and analyzed by HPLC at 24-hour intervals for five days. The chromatograms were analyzed by the Gaussian deconvolution software program PeakFitä and the component peaks grouped into seven classes: low molecular weight (LMW, <50 kDa), sub-alpha (50-80 kDa), a chains (80-125 kDa), b chains (125-225 kDa), g chains (225-340 kDa), e fraction (340-700 kDa), z fraction (700-1000 kDa), d chains (1000-1800 kDa) and a microgel fraction (>1800 kDa). The changing percentage contents of these classes were subjected to kinetic analysis. Results. In the control gelatin solution, the content of lower molecular weight classes (<340 kDa) remained approximately constant with time. Medium molecular weight classes (340-1800 kDa) underwent a renaturation process, resulting in a first-order increase in the content of the microgel fraction (rate constant kmicrogel = 0.1x10-2 hr-1) and first-order decreases in the d (kd = -0.3x10-2 hr-1) and e (ke = -0.1x10-2 hr-1) fractions. Gel filtration chromatography separated the microgel, medium and low molecular weight fractions. On incubation, these fractions demonstrated first order decreases in the percentage content of both microgel (kmicrogel = -4.1x10-2 hr-1) and medium molecular weight material (kd = -5.1x10-2 hr-1, kz = -4.1x10-2 hr-1, and ke = -5.6x10-2 hr-1), with a corresponding increase in a chains (ka = 2.6x10-2 hr-1). Conclusions. The medium molecular weight polymers in an unfractionated gelatin solution exhibited a tendency to renature towards higher molecular weight structures. However, our results suggest that the proteins are stabilized by being in equilibrium with the monomeric a chains. When this equilibrium is disturbed by fractionation, the system undergoes changes in its composition in order to re-establish its original state in accordance with Le Chatelier’s principle. These changes occur at a much faster rate than the renaturation process, thereby swamping any renaturation kinetics.