The intermetallic compound CeNi2Al5 is a magnetic dense-Kondo compound exhibiting a magnetic phase transition at 2.6 K. The temperature dependence of the specific heat of a single crystalline sample CeNi2Al5 has been measured in the temperature range from 0.7 K to 3 K under a magnetic field parallel to the b axis up to 8 T. The H-T phase diagram has been determined from the anomalies in the temperature dependence of the specific heat.