Adherence is a determining factor for the success of iron supplementation programs in pregnant women. There are several factors that influence adherence, the most significant of which are knowledge of pregnant women and counseling by health workers. This systematic review of the literature aims to identify the effect of knowledge and counseling on pregnant women's adherence to taking iron supplementation. Literature searches were conducted through four main electronic databases, namely PubMed, Scopus, ScienceDirect, and Web of Science. Fourteen studies met the inclusion criteria and were eligible for review. The PRISMA approach is used in critically evaluating articles. Literature quality assessment was carried out using the quality assessment tool for quantitative studies from the EPHPP (Effective Public Health Practice Project). Findings are collected and summarized systematically. The results are categorized into two major themes. Consistent with previous research, this review explains that knowledge and counseling have a significant effect on adherence. Good knowledge increases adherence by two to five times, and counseling by health professionals increases adherence by two to four times.