Aluminum toxicity is the most widespread form of metal toxicity to plants in soil acids, initially causing inhibition of root elongation and blocks absorption of water and nutrients. According to this fact that soybean has been widely used in industry, this study investigated the effects of aluminum toxicity on biochemical factors in two varieties of Williams and Katoul of soybean plant. The study was carried out in a randomized design with aluminium (0, 200, 500, 700 µM) treatments and four replications in hydroponic culture. Results of biochemical tests showed that aluminum reduced the content of photosynthetic pigments, flavonoids, phenolic compounds, anthocyanins and reduced sugars in both cultivars of soybean. The proline content decreased with increasing aluminum in var. williams, but at var. katoul increased. It seems that G. max var. katoul suffers less than var. Williams. As regards, proline accumulation under Al stress to be generally higher in G. max var. katoul; hence, these results suggest that var. katoul is more resistant than var. Williams.