The actions are based on an increase in number of reports ranging from years ago to the present, Activision said in a letter to employees.
The owner of "Call of Duty" and "Candy Crush" franchises added it would expand its ethics and compliance team in order to create a "more accountable workplace and culture". The company will add 19 full-time roles to the team.
"Two of those roles will be specifically dedicated to overseeing investigations related to the EMEA (Europe, the Middle East and Africa) and APAC (Asia Pacific) regions," it added.
Activision said a report could be submitted anonymously, and that there was zero tolerance for retaliation of any kind. It added that the company would "terminate or discipline" individuals violating its policies.
The sacking of 20 employees was first reported by the Financial Times.
Earlier in September, Activision Blizzard and the U.S. Equal Employment Opportunity Commission (EEOC) said they had reached an agreement to settle claims over sexual harassment and discrimination in the company's workplace.
The EEOC, which has been investigating allegations of sexual harassment, discrimination and retaliation at Activision for three years, found that the company failed to take corrective and preventive measures on sexual harassment complaints, according to a filing in the U.S. District Court of the Central District of California.
The company also said last month it was continuing to work with regulators on addressing and resolving the workplace complaints it has received.
(Reporting by Tiyashi Datta in Bengaluru; Editing by Maju Samuel)