Background: Silver Diamine Fluoride (SDF) is utilized to halt the progression of dental caries without inflicting pain or necessitating invasive procedures. Regrettably, it discolors the decayed teeth and imparts a black hue to them. Potassium iodide (KI) causes tooth-colored reactions upon interaction with silver ions. The aim of this study is to evaluate the effect of SDF with or without KI on the adhesion and microleakage of pit and fissure sealant (FS) to tooth enamel. Methods: Sixty extracted sound human permanent caries-free molars or with grade 1 caries according to the modified International Caries Detection and Assessment System II (ICDAS II) were randomly divided into three groups: FS, SDF + FS and SDF + KI + FS. Adhesion and microleakage tests were done for each group, which consisted of 20 teeth. To test FS adhesion to tooth structure, the specimen was decoronated 2 mm below the cementoenamel junction, fixed in acrylic and subjected to a universal testing machine to determine the shear bond strength (SBS), detachment resistance and adhesive remaining index. For the microleakage test, specimens were immersed in a 1% methylene blue solution for 24 hours. Results: The FS group showed the highest mean SBS (35.12 ± 1.13 Mpa), followed by the SDF + KI + FS group (27.33 ± 1.1 Mpa), then the SDF + FS group (18 ± 0.9 Mpa) with a statistically significant difference between the three groups. However, the adhesive remnants index (ARI) index score and microleakage test showed no statistically significant differences between the three groups. Conclusions: Pretreating fissures with SDF with or without KI before applying sealant may adversely affect the adhesion to the tooth structure and not affect the microleakage of the FS.