A method was developed for the determination of gallium in coal and coal fly ash by electrothermal atomic absorption spectrometry using slurry sampling and nickel chemical modification. In the presence of nickel modifier the integrated absorbance for gallium was improved by a factor of 2.46 and matrix interferences with the absorption signals were eliminated, and hence similar atomization profiles were obtained for gallium in slurries and in aqueous standard solutions. Therefore, calibration using aqueous standards could be applied. The recommended method was applied to the determination of gallium in real samples. The data obtained by slurry sampling were in good agreement with the certified values or with those obtained after pressure attack of the samples. The relative standard deviations for ten replicate determinations were in the range 2.1–5.7% for gallium in coal and coal fly ash for gallium concentrations of 1.05–59.7%µg g^–1.