The aim of this study was to demonstrate thermogravimetric analysis (TGA) as a potential method for monitoring biodiesel production. Soybean oil and commercial biodiesel were mixed in different proportions by weight. Mixtures of different biodiesel/soybean oil ratios were also created by interrupting a base-catalyzed transesterification process for producing biodiesel at various times. The mixtures produced by both approaches were analyzed with TGA. The results were then compared with data obtained by proton nuclear magnetic resonance spectroscopy ( ¹HNMR spectroscopy). The relative weight losses in both sets of mixtures we generated correlated well to the proportion of biodiesel present in the sample. The results from both analytical methods were in good agreement and within a deviation of 5%. Thus, TGA is a simple, convenient and economical method for monitoring biodiesel production.