It was observed that 1-phenylalanine and aspartame form thermoreversible gels in aqueous solutions (which include crystals) through nonagitated crystallization. FT-IR spectra of aspartame gel-crystals indicated that the possible interactions involved in gel formation are hydrogen bonding between the carbonyl and the amine groups and electrostatic interactions between NH3+ and COO-. For gel-crystals of 1-phenylalanine, the main interaction involved was electrostatic interaction between NH3+ and COO-. According to the thermal analysis of aspartame and 1-phenylalanine solutions, the gel-melting temperature increased with increasing heating rate and the gel-crystallization temperature decreased with increasing cooling rate.