Use of organic inputs and suitable density of corm are two agronomic important factors to achieve the maximum yield in saffron (Crocus sativus L.). In order to study the effects of spent mushroom compost (SMC) levels and corm densities on agronomic characteristics, flower and stigma yields of saffron, a greenhouse experiment was conducted as factorial layout based on a randomized completed block design with three replications at the Campus of Agricultural Research Greenhouse, Ferdowsi University of Mashhad during two years of 2009 and 2010. Factors were three levels of SMC (0, 60 and 120 t.ha-1) and three corm densities (50, 100 and 150 corm.m-2). Leaf and tunic dry weights, leaf length, number and weight of corms in three groups (2-4, 4-8 and 8-16 g), corm diameter, flower number, flower fresh weight and stigma yield of saffron were measured. Results indicated that the simple effects of SMC levels and corm densities on leaf and tunic dry weights, leaf length, corm diameter, number and weight of corms in different groups, flower number, flower fresh weight and economical yield of saffron were significant (p≤0.05). By increasing in corm density, growth, flower production and yield of saffron were enhanced. By increasing in corm density from 50 to 150 corms.m-2, flower and stigma yield were decreased up to 12%. Application of 60 t.ha-1 SMC enhanced growth characteristics and economical yield of saffron and these traits were declined afterwards. The maximum and the minimum flower fresh weight and stigma yield of saffron were observed in 60 t.ha-1 SMC (55.05 and 0.51 kg.ha-1) and control (46.22 and 0.43 kg.ha-1), respectively. Therefore, it seems that the application of appropriate levels of organic inputs and corm density must be considered for this cash crop.