Single crystals of triglycine sulfate (TGS) doped with various L-form amino acids have been prepared. Doping effects on the crystal morphology and the ferroelectric domain structure, and the generation of internal bias field E b were investigated. For crystals grown from solutions with L-valine, L-leucine, and L-isoleucine, both the morphology and the domain structures were resemble to pure TGS and the generation of E b was not realized. Doping of L-threonine, L-cysteine, L-asparagine, L-aspartic acid, and Lmethionine caused obvious effect on the morphology. The effect on the domain structure and the generation of E b in these crystals were considerably different from those in L-alanine doped crystals.