The linewidth enhancement factor (LEF) and nonlinear gain coefficient of an InAs/AlGalnAs quantum dot (QD) laser are measured using an injection locking technique. The nonlinear gain coefficient was found by curve-fitting the measured LEF as a linear function of the output power. The LEF of the InAs/AlGalnAs quantum dot laser was measured to be 1.2 to 8.6 at output powers from 2 to 10.2 mW, leading to a corresponding nonlinear gain coefficient of 1.4 × 10-14 cm3. This value for the nonlinear gain coefficient is three orders of magnitude higher than the typical quantum well nonlinear gain coefficient of 10-17 cm3. Consequently we expect that the dynamics under optical injection and external feedback of this type of quantum dot laser will be dramatically different than in quantum well lasers, suggesting that a careful re-examination of the dynamics of this type of laser is needed.