Axon

1. It is long uniformly thickened fibre like process of a neuron.

2. It is always covered with a sheath (e.g., medullary sheath).

3. Nissl’s granules are absent. Neuro fibrils are, however, present.

Dendrite

1. It is a short tapering process of a neuron.

2. A sheath is absent. 

3. Both Nissl’s granules and neurofibrils are present.