In this work, the combustion of heavy oil and its emulsions with water, in the cement kilns, was investigated in experiments on an industrial scale. The performance of the cement rotary kilns, used in Tartous Company for cement and construction materials, was studied when they were employed to be operated with heavy fuel oil (HFO) and with the water phase of emulsified heavy oil containing 8 vol. % water and 92 vol. % heavy fuel oil (HFO). The emulsified water/heavy fuel oil (W/HFO) with 8 vol. % of water content showed no separation and contained the smallest and most homogeneous water-in-HFO (W/HFO) droplets after stability tests. Four rotary kilns have been operated for 4 months with a regular heavy fuel oil HFO and W0.08/HFO0.092. It has been found that the micro-explosion, observed in W0.08/HFO0.092, improved the kiln efficiency and reduced the fuel consumption by 10.31% in the case of normal feeding while the fuel saving increases with decreasing the feeding rate and reaches 12.99 at low feeding rate. The effect of emulsified fuel on the composition of Portland cement clinker that produced in Tartous Company for cement and construction materials using these two types of fuels is investigated. It is found that the influence is practically negligible on the Alite and Ferrite phases of clinker composition while the influence on the other two phases is important.