The purpose of this research is to study the decomposition activity of hyacinth and straw decomposed by activator, and the effect of the activator and the organic sources to decomposition period and compost quality. The treatment was arranged in 2x3 factorial Completely randomized design. The first factor is the type of the organic sources which consists of two levels which are hyacinth and straw. The second factor is the activator types which consist of three levels which are cow mature was used as natural activator, while Stardec (powdered) and EM4 (liquid) as a artificial ones. Organic matters were incubated for 5-6 weeks then physics changes (temperature, color and consistency), microbiological changes (total amount of fungi and bacteria) and chemical changes (C/N ratio, total acid and pH) were measured every week. The result shows that chemical changes during decomposition is influenced by the type of the activator which fungi and bacteria contains are different. Aplication of artificial activatos EM4 enhanced the maturity rate of decomposition which is shown with the decreasing of C/N ratio and physical changes of the compost. The straw-compost had betterquality according to the C/N ratio (8,81) than the straw-compost (11,28).