Defect configurations in as-grown mixed crystals of ammonium-potassium sulphate have been revealed by chemical etch technique with greater details for the first time. Interesting features like symmetrical pyramidal pits, circular terraced pits, row of closely spaced pits forming low angle tilt boundary indicating branching of dislocations etc. were clearly observed using aqueous solutions of various inorganic salts (etchants) applied for different timings. It is found that addition of a salt generally promotes the formation of good pits. The results are briefly interpreted in the light of Cabrera's thermodynamic theory of dislocation etch pit formation. The optical and scanning micrographs show a good correspondence between formation of etch pits and dislocations.