Oral nutritional supplements (ONS) administered to malnourished elders and other patients contain high-levels of carbohydrates that could be a potential risk factor for dental caries. This study aimed to evaluate the cariogenic potentials of ONS using intraoral plaque telemetry. Ten ONS were tested on five healthy volunteers (mean age: 76.8 ± 9.15 years). Participants were requested to refrain from performing oral hygiene 3-7 days prior to testing. The pH-value below the dental plaque on the tooth was measured while the ONS was being consumed. After neutralizing the participant's saliva, a control solution (10% sucrose) was administered and telemetry measurements were repeated. Mean relative cariogenicity (RC) was calculated for each ONS. ANOVA and post hoc tests were used for statistical analyses (p < 0.05). All ten ONS were potentially cariogenic on enamel with an overall RC of 0.519 ± 0.35 (Range: Min = 0.31 ± 0.16; Max = 1.00 ± 0.34). RC differed significantly between the ONS (p = 0.002). RC was lower in ONS that contained high-protein (p = 0.018). RC was not influenced by other factors such as readily consumable (p = 0.102), flavor (p = 0.869), consistency (p = 0.126), fiber containing (p = 0.134), style (p = 0.112), and age of plaque (p = 0.339). The ONS administered to elders and malnourished patients are potentially cariogenic. It is imperative that the administration of ONS must be based on individual needs to potentiate a maximum benefit. Wherever possible, an attempt to limit the use of high-carbohydrate containing ONS must be practiced along with the adoption of suitable preventive measures to arrest the development and progression of caries.