Diatomaceous earth has a low density and this makes the material useful in producing lightweight aggregates. Therefore, this research was conducted to study the mechanical properties including the compressive strength, modulus of elasticity, splitting tensile strength, and flexural strength as well as the absorption of the lightweight concrete produced from the lightweight aggregates. Moreover, two methods were used to produce lightweight aggregates and the first was by burning diatomaceous earth chunks at a temperature of 650 °C and crushing them with a stone crusher while the second involved refining the material to make pellets after which it was burned at 650 °C. Two types of pellet were produced using diatomaceous earth only and with the addition of 5% sawdust due to the fact that the significance of this study was to utilize the diatomaceous earth as lightweight aggregates in lightweight concrete production. The lightweight concrete produced from the aggregates made using the first method had a density ranging between 1121 kg/m³ to 1181 kg/m³, however, based on its strength it can only be used as a non-structural element and an insulating material. Meanwhile, the concrete produced from the aggregate made using the second method as coarse aggregate and river sand as fine aggregate had a density of 1832 kg/m³ and based on its strength it can be classified as a lightweight structural concrete. Furthermore, the addition of 5% sawdust to the pellets had the ability to improve the mechanical properties, reduce the absorption, and decrease the density of the lightweight concrete.