The kinetic mechanism of L-asparagine (L-Asn) action on t-aspartic acid (L-Asp) crystal growth, namely the face-selective effect of L-Asn on the I.-Asp crystal growth rate in each direction, was examined. In the a-axis direction, the effect of L-Asn on the L-Asp crystal growth rate was small. Enhancement and inhibition of t-Asp crystal growth, and interestingly the dissolution of the L-Asp crystal face, were observed in the b-axis direction, depending on the amount of L-Asn added. In the c-axis direction, the L-Asp crystal growth rate decreased with the increase in the amount of L-Asn added, and the experimental results were well fitted with a Langmuir adsorption isotherm. The study showed that there were crystal growth conditions where enhancement and inhibition, as well as inhibition and dissolution, coexisted in the presence of an additive with a structure similar to the growing crystal. (C) 2015 Elsevier B.V. All rights reserved.