Rhododendron arboreum subsp. zeylanicum is an endemic woody plant found in Sri Lanka. Although it is a vulnerable plant and has ornamental value. Rhododendron species naturally grow from seeds and regeneration rate is low. The vegetative propagation of most woody rhododendrons is slow. The investigation of seed germination is important for the conservation of this species. The first experiment was carried out to study the effect of growing media (Unsterilized native soil, native soil: coir dust (1:1), native soil: leaf mould (1:1), coir dust: sand (1:1), native soil: sand (1:1), and clay soil) and to compare the impact on two geographical locations (Peradeniya and Hakgala) for in vivo seed germination. The second experiment was carried out to investigate the effect of different culture media (Anderson (ADW), autoclaved distilled water + agar, ½ strength Murashige and Skoog (MS), and full-strength MS) with two different sterilization methods (15% Clorox with few drops of Teepol for 15 minutes and 20% Clorox with few drops of Teepol for 10 minutes) on in vitro seed germination. The germination percentage was significantly affected by the location and growing media. The highest germination percentage was recorded in coir dust: sand medium (1:1). Hakgala is better than Peradeniya for in vivo seed germination. In the in vitro seed germination, the lowest germination and the highest contamination percentages were recorded in the full-strength MS medium. The highest root length was recorded in the seeds treated with ADW + agar. And the highest plant height was recorded in the seeds treated in ADW + agar with 20% Clorox and few drops of Teepol for 10 minutes