Phytocystatins are proteinaceous competitive inhibitors of cysteine peptidases involved in physiological and defensive roles in plants. Their application as potential therapeutics for human disorders has been suggested, and the hunt for novel cystatin variants in different plants, such as maqui (Aristotelia chilensis), is pertinent. Being an understudied species, the biotechnological potential of maqui proteins is little understood. In the present study, we constructed a transcriptome of maqui plantlets using next-generation sequencing, in which we found six cystatin sequences. Five of them were cloned and recombinantly expressed. Inhibition assays were performed against papain and human cathepsins B and L. Maquicystatins can inhibit the proteases in nanomolar order, except MaquiCPIs 4 and 5, which inhibit cathepsin B in micromolar order. This suggests maquicystatins’ potential use for treating human diseases. In addition, since we previously demonstrated the efficacy of a sugarcane-derived cystatin to protect dental enamel, we tested the ability of MaquiCPI-3 to protect both dentin and enamel. Both were protected by this protein (by One-way ANOVA and Tukey’s Multiple Comparisons Test, p < 0.05), suggesting its potential usage in dental products.