Spherulite growth rates have been measured in two polyamides, 66 and 6 nylon, at temperatures ranging from 38 to 141° below the melting points using a moving photomicrographic technique. At constant temperature, the spherulite radius increases at a constant rate. This isothermal growth rate constant is temperature dependent, having low values just below the melting point, passing through a maximum on further supercooling and decreasing to negligible values at room temperature. These facts indicate that spherulite growth is not a diffusion controlled process. A reasonable interpretation of the data has been obtained using the concept of growth by two‐dimensional surface nucleation. A theoretical expression for the temperature dependence of the growth rate based on this concept has given good agreement with the experimentally determined values.