Apreliminary study on February 6 , 2014 showed that fly density per block grill was 7 flies. This indicated the presence of problems on density of flies. This study tried to provide innovation in wax to reduce the density of flies, ie by adding citronella oil. This study's aims were: (1) to determine the effect of citronella oil in the solid wax towards the decreasing density of flies; (2) to know the decreasing density of flies with citronella oil concentration 8%, 10% and 12%; and (3) to know the most effective concentration. The method used was experiment design with Pre and Post Test With Control Group Design. The population in this study were 85 food stalls located along Depok Beach and flies. The sampling method was using purposive sampling food stalls, using incidental sampling flies. The results of the research was analyzed using a One Way ANOVA. The results of this study were as follows: (1) When the candle contained citronella oil as much as 8%, it could reduce fly density as much as 18,11%; (2) When the candle contained citronella oil as much as 10%, it decreased fly density as much as 29,86%; and (3) When the candle contained citronella oil as much as 12%, it reduced fly density as much as 44,38%. Statistical analysis showed p-value 0.003 <0.05, meaning there was a significant influence of the addition of citronella oil in the candle towards the decrease of fly density in the food stalls. Thus, the conclusion of this study is there is a significant effect concerning the addition of various concentrations of citronella oil in the candle to decrease fly density in the food stalls. The most effective concentration of citronella oil in the candle is 12%.