This research was to study the mixture ratio of lightweight interlocking blocks from sludge mixed with 3 types of pozzolanic materials such as bagasse ash, diatomite, and rice husk ash by calculating the cement mixture ratio with sludge replacement percentages of 20 80 by weight of cement when obtaining the appropriate mixture ratio with respect to compressive strength that passed the standard and lightweight before replacing the sample with 3 types of pozzolanic materials at 10 % sludge by weight for determines the mixture ratio of lightweight interlocking blocks . Based on the study results, the sludge replacement caused a decrease in compressive strength for all ratios. In this research, the cement sludge mixture ratio of 30:70 was, therefore, chosen to replace 3 types of pozzolanic materials. According to replacement results, it showed that the replacement by bagasse ash yielded higher compressive strengths than control samples for all ratios, where as the replacement by diatomite and rice husk ash yielded a decrease in compressive strength when compared to control samples. Regarding weight, replacement by 3 types of pozzolanic materials resulted in lightweight for all ratios. As for testing of masonry prisms, it demonstrated that replacement by bagasse ash in the cement sludge bagasse ash ratio of 30:40:40 yielded the maximum compressive strength when compared to interlocking blocks from 3 markets, corresponding to the standard of the non load bearing interlocking block that determines the compressive strength not less than 70 ksc.