Aim of the work: This in vitro study was performed to assess the efficacy of Papacárie in comparison with the conventional rotary instruments to remove carious lesion in primary teeth. Microbiological study, histological picture and microhardness of dentin were evaluated after caries removal with both methods.   Materials and Methods: Twenty primary carious molars were selected for this study. Ten molars were prepared for the microbiological and histological assessment and the other ten were prepared for the microhardness assessment. After caries removal with the conventional method and Papacárie, the samples were subjected to microbiological analysis with culture test, histological analysis and to Vicker's hardness test.   Results: The conventional method and Papacárie are efficient in caries removal. The culture test has revealed that both methods have reduced Streptococcus mutans count significantly with a percentage of reduction of 84.686% & 85.06% respectively. Also, the conventional method and Papacárie have reduced Lactobacilli count significantly with a percentage of reduction 83.227% & 83.872% respectively. Light microscopic analysis showed that the Papacárie preserves the dentin structure more than the conventional method and the bacterial deposits left in the dentinal tubules were less in case of Papacárie. The microhardness test revealed that the mean hardness of dentin after caries removal with the conventional method was 75.49 Kg/mm2 and after caries removal with Papacárie was 76.51 Kg/mm2 with no statistically significant difference between both methods.   Conclusion: It was concluded that Papacárie is efficient in caries removal, has antibacterial action on Streptococcus mutans and Lactobacilli, and preserves the dentin structure and microhardness.