Abstract Different levels of sodium hydroxide (NaOH) or ammonia bicarbonate (NH 4HCO 3) were applied to rice straws to investigate the effects on histological dynamic change of stem epidermis before and after in sacco degradation using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The papillae, wart-like structures and micro-hairs on the cuticle layer of stem epidermis were crimped by treatment with NaOH above 30 g/kg straw dry matter, but were not crimped in NH 4HCO 3-treated stems. A part of the cuticle wax and silica layer was breached at high dosages of NH 4HCO 3. Epidermis was degraded in NaOH-treated stem, but was still observed in untreated or NH 4HCO 3-treated stems, even after rumen incubation for 48 h. Degradation was observed more clearly under TEM than under SEM. Micro-hairs of both untreated and treated stems were not degraded or detached from the epidermis earlier than other epidermal structures. Results indicate that the cuticle wax silica layer of rice stem epidermis is an important barrier to rumen degradation, but pretreatment with NaOH or NH 4HCO 3 may dissolve (NaOH) or crack off (NH 4HCO 3) this layer, and that changes increase in a dose-dependent manner. With the dissolving of the cuticle wax layer, the epidermis in the NaOH-treated stems could be degraded by rumen microorganisms, whereas only the breach of the cuticle layer in NH 4HCO 3-treated stems did not result in degradation of epidermis leading to a lesser positive improvement on rumen digestion versus NaOH treatment.