The attack killed nine people and wounded hundreds of others. In the report released on Monday, nine chemical attacks had taken place between November 17th to December 13th, and among the fatalities were four children.
The Rights group said it had interviewed witnesses, collected photos and reviewed video footage that showed government helicopters dropped chlorine bombs. 200 people were injured during the operation in the opposition northern part of the city.
The deadliest bombings took place in the Sabhur neighborhood on 20th November, killing six members of the same family including four children. A video made by the Shabha Press Agency shows the lifeless bodies of the children.
Aleppo was once Syria's bustling commercial hub but has since been divided between a government-held west and a rebel-controlled east since 2012.
The bid to retake the city by the government was backed by Russian forces, although HRW did not find the Russians culpable of the chemical attacks.
Attacks took place in playgrounds, clinics, residential houses, and streets. People were left gasping for air, vomiting while others lay unconscious. The bombs were dropped where government forces were expected to advance.
"The pattern of the chlorine attacks shows that they were coordinated with the overall military strategy for retaking Aleppo, not the work of a few rogue elements," said Ole Solvang, HRW's deputy emergencies director.