The Central Asian country's long-reigning president Nursultan Nazarbayev, 77, had signed into law amendments "aimed at improving legislation on information and communication issues," his office said on Thursday.
Among the changes that have alarmed journalists and civil rights activists was one demanding news websites identify users posting comments under articles and retain their data for a period of three months.
Another controversial amendment obliges journalists to receive permission from persons mentioned in their articles to publish information that could be classified as "personal, family, medical, banking, commercial and other legally protected secrets."
Kazakhstan's government had journalists and civil activists involved in discussion of the law but ultimately ignored key objections.
The law earlier sailed through both houses in Kazakhstan's parliament.
Nazarbayev has ruled over Kazakhstan with very little opposition since before independence from the Soviet Union in 1991.