In this study, the microstructure and crystallization kinetics of binary and ternary mixtures of milk fat fractions during isothermal crystallization at 5, 15, and 20 °C were characterized using polarized light microscopy and the Avrami model. Results showed that for both binary and ternary mixtures, high concentrations of the high-melting fraction result in the formation of rod or needle-like crystals (i.e., one-dimensional growth and low values of Avrami index, n) while at relatively higher concentrations of the middle-melting and low-melting fractions, multi-dimensional crystal growth is favored (i.e., higher n values). On the effect of temperature, for binary mixtures, it was found that at high undercooling conditions (5 °C) one dimensional growth is favored while for ternary mixtures, increasing the crystallization temperature (i.e., decreasing supersaturation) from 15 to 20 °C results in large differences in crystal structure. Mechanisms for the observed behavior are also suggested.