Abstract. Mulati A, Supriyono, Wiryowidodo W. 2017. Effect of type of seedling media and duration of synthetic auxin immersion on germination and initial growth of papaya (Carica papaya) seedlings. Cell Biol Dev 1: 64-70. Papaya (Carica papaya L.) is a well-known fruit plant with high economic value. The uniformity of germination and initial growth must be considered to get normal mature plants. Using appropriate seedling media and synthetic auxin can support the germination and initial growth of papaya seedlings. This study aimed to determine the effect of the type of seedling media and the duration of immersion of synthetic auxin, and the combination that had a positive effect on germination and initial growth of papaya seedlings. This research was conducted in Badranrejo, Kemiri, Mojosongo, Boyolali, and the Laboratory of the Faculty of Agriculture, Sebelas Maret University, Surakarta, from April to July 2009. This study used a Completely Randomized Design (CRD) with two treatment factors and three replications. The first factor was the type of seedling media: soil, soil + farmer-produced cow manure (1:1), soil + self-produced cow manure (1:1), and soil + farmer-produced cow manure + self-produced cow manure (1:1:1). The second factor was the immersion time in synthetic auxin: 0 hours, 1 hour, 2 hours and 3 hours. Data were analyzed by analysis of variance and if there was a significant difference, proceed with DMRT 5%. The results showed that the interaction between seedling media and immersion time in synthetic auxin did not occur. Therefore, adding cow manure as a medium is unnecessary, especially for papaya seed germination. Synthetic auxin immersion from 1 to 3 hours did not increase all variables of germination and initial growth of papaya seedlings.