The father, a casual worker, has been arrested.
According to police, Hari Om, a resident of Gujarat, had come to his in-law's house in New Usmanpur area in east Delhi to take his wife and son back to his home.
His unwilling wife resisted and a quarrel ensued between the two. Om then flung his son from the balcony to "teach his wife a lesson". The child was taken to Guru Teg Bahadur Hospital Hospital but died on arrival, said an officer yesterday.
Police said Om was angered with his wife's refusal to return with him and did not want his son to stay with the mother.
His wife had left his house after a dispute between them, said an officer.