New opticallyactive organosilicon compounds such as (benzylmethylphenylsilyl)acetic acid (1) and (ethylmethylphenylsilyl)acetic acid (2) were synthesized. Application of these acids as the optical purity determining agents for chiralamines and alcohols were successfully carried out. In addition, it was also revealed that opticallyactive (benzylmethylphenylsilyl)methylamine (3) and [benzylmethyl