The effect of the interaction of varying chicken manure supplement levels with three different solid sisal wastes substrates on sporocarp cap lengths and diameters, stipe lengths and diameters and dry weights of Coprinus cinereus (Schaeff) S. Gray s.lat Coprinus cinereus (Schaeff) S. Gray s.lat is an indigenous Tanzanian edible and medicinal mushroom, which grows in the wild on decomposed sisal wastes heaps. In the laboratory, it was cultivated on three types of sisal wastes substrates each supplemented with varying chicken manure concentrations 0, 5, 10, 15, 20 and 25% using solid-state fermentation bioreactors. The results showed that the interaction of sisal dust, sisal fibres and sisal decortications leaves wastes substrates with chicken manure at varying concentrations, produced a highly significant effect (p < 0.05) on cap lengths and diameters, stipe lengths and diameters and dry weights of C. cinereus (Schaeff) S. Gray s.lat. The interactions of sisal dust waste with 5% chicken manure concentration induced longest mean cap length and widest mean cap diameter. On the other hand, the interaction of sisal leaves decortications wastes with 25% chicken manure concentration produced heaviest sporocarps mean dry weight. These findings for the first time illustrate importance of chicken manure supplementation in C. cinereus (Schaeff) S. Gray s.lat cultivation on sisal decortications wastes substrates.Key words: Coprinus cinereus, chicken manure, solid sisal wastes, sporocarps, pileus, stipe.