Objective: To investigate the effectiveness of two treatment methods, namely topical applications of silver diamine fluoride (SDF) solution and a high fluoride releasing glass ionomer, in arresting dentine caries in primary teeth. Methods: 212 preschool children, aged 3-4 years, in a rural area in Southern China were randomly allocated to one of three groups for treatment of the carious cavities in their primary teeth: Gp1-annual application of SDF, Gp2-semi-annual application of SDF, and Gp3-annual application of a high fluoride releasing glass ionomer. Treatments were provided in the kindergartens. Information on the children's demographic background, oral hygiene and snacking habit was collected by questionnaires. Follow-up examinations were carried out every six months by an independent examiner. Intra-oral LED light, mouth-mirrors and sharp probes were used. Treatment success was recorded when the glass ionomer covered the whole lesion or the caries lesion was arrested, i.e. hard to probing with a light force. Generalized Estimating Equation (GEE) approach was used to account for the within-subject clustering effect when assessing the effects of treatment group, tooth position, surface and other background factors on the outcome. Results: After 24 months, 178 (84%) children were examined. The success rates were 79.2%, 90.7% and 81.8% for Gp1, Gp2 and Gp3, respectively (Chi-square test, p=0.007). Children's background and behavioral factors had no significant effects on the treatment outcome. The lesions in Gp2 were more likely to become arrested compared to those in Gp1 (OR=2.98, p=0.007) or Gp3 (OR=2.65, p=0.001). Success rates were also higher for lesions in the anterior teeth (OR=5.55, p<0.001) or in buccal/lingual smooth surfaces (OR=15.6, p=0.004). Conclusion: The 24-month success rates of the two treatment methods are high in this study population, with that of semi-annual application of SDF being the highest. Success of caries arrest treatment varies with tooth position and the surface involved.