Objective To investigate the effects of composite probiotic tablet candy containing Lacticaseibacillus rhamnosus CCFM1070 and Ligilactobacillus salivarius CCFM1215 on Streptococcus mutans levels and the microbial community structure in children with early childhood caries (ECC).Methods Forty-three ECC patients are randomly assigned to either a probiotic group (n=21) or a placebo group (n=22). Following standard dental treatment, a 4-week intervention is administered. Quantitative PCR (qPCR) and 16S rRNA sequencing are used to systematically analyze microbial dynamics in saliva and dental plaque at baseline (Day 0) and post-intervention (Day 28).Results Following the intervention, the levels of S. mutans in saliva and dental plaque of the probiotic group significantly decrease from 0.78 and 0.97 lg (DNA copies/ng) to 0.71 lg (DNA copies/ng) (P<0.01) and 0.90 lg (DNA copies/ng) (P<0.05), with a greater reduction than the placebo group. Probiotic intervention significantly decreases the relative abundance of cariogenic genera like Streptococcus and increases that of commensal genera like Fusobacterium. This effectively improves the oral microbial structure and microbial richness in ECC patients, promoting oral health.Conclusion The findings demonstrate that composite probiotic tablet candy can ameliorate caries progression by inhibiting cariogenic pathogens and enriching oral commensals to remodel oral microbial homeostasis.