Abstract: The objective of this research was to reduce ruminal protein degradability of Wolffia meal (Wolffia globosa L. Wimm.) by roasting at 150°C for 2 to 8 min. Two Thai-indigenous x Brahman crossbred cattle were used to determine the in situ ruminal degradability of heat-treated Wolffia meal. The ruminal degradation characteristics of Wolffia meal were determined using nylon bags incubated in rumen in reverse order for 72, 48, 24, 12, 8, 4 and 2 h. The results found the decreased rapidly soluble Crude Protein (CP) fraction (p<0.05) and the increased potentially degraded CP fraction (p<0.05) of Wolffia meal roasted at 150°C for 6 to 8 min. However, protein degradability of Wolffia meal was not reduced by heat treatment. The results indicated that roasting at 150°C for 6 to 8 min could not protect Wolffia meal’s protein degradation by rumen microorganism.