The polylactic acid (PLLA) is commonly used in the biomedical application. The physical and mechanical properties of PLLA depend on the molecular weight, crystallinity, and synthesis. In this work, we study the PLLA crystallization kinetics. One of the main attractive of these polymers is that its degree of crystallinity can easily be modified, from amorphous state to a high crystallinity degree. In this study a new technique is applied to follow the crystallization kinetic. An optical microscope with cross polarizers, warming plates and video camera were used. A series of images were obtained under isothermal conditions to observe the growth spherulite. Since an image is composed by pixels and each pixel has a value from 0 to 255, which represents gray intensity, being zero for black and 255 are white. Then, the pixels average versus time was plotting and from the plots crystallization kinetic and secondary crystallization are easily obtained.