Abstract Amino acids mixed TGS crystals are of interest due to their high pyroelectric coefficient and low dielectric constant. Partial substitution of phosphate has resulted in triglycine sulpho-phosphate (TGSP), a mixed crystal with improved pyroelectric figure of merit. In order to study the effect of amino acids on the ferroelectric properties of TGSP, we have substituted l-alanine (ATGSP), l-valine (VTGSP), l-asparagine (ASP-TGSP) and l-arginine (ARG-TGSP) in pure TGSP The pyroelectric studies and P-E hysteresis measurements carried out on these mixed crystals are reported. A scanning electron microscope in the secondary electron emission mode has been employed to visualize the domains on the mixed crystals.