The aim of this study was to evaluate the shear bond strength (SBS) and microleakage of bacterial cellulose nanocrystals (BCNCs) incorporated into conventional glass ionomer cement (CGIC) when bonded to deciduous dentin. Sixty primary first and second molars with class I cavitated dentinal lesions were preserved and randomly allocated into two groups based on the technique used for caries removal. Group 1 utilized the conventional approach for caries removal, while Group 2 used Carie Care™ for caries removal. Each of these groups was further divided into two subgroups based on the type of restoration received. Microleakage and failure mode assessments were performed using a stereomicroscope, while SBS testing was conducted using a universal testing machine. The SBS and microleakage scores were analyzed using one-way analysis of variance (ANOVA) and Tukey post hoc test with a significance level of p=0.05. Specimens from Group 1A (conventional approach+CGIC) presented the highest scores of marginal leakage, while Group 1B (conventional approach+BCNCs-modified CGIC) demonstrated the lowest values of microleakage. Additionally, samples from Group 2B (Carie Care™+BCNCs-modified CGIC) revealed the highest bond integrity scores. The incorporation of BCNCs into CGIC had a positive impact on both shear bond strength and marginal leakage when bonded to the dentin substrate. This modification improved the performance of the glass ionomer cement, enhancing its applicability in dental restorations.