Purpose of work The purpose of this study is to report a thermostable lambda-carrageenase that can degrade lambda-carrageenan yielding neo-lambda-carrabiose at 75 A degrees C. A thermophilic strain Lc50-1 producing lambda-carrageenase was isolated from a hot spring in Indonesia and identified as a Bacillus sp. The lambda-carrageenase, Cga-L50, with an apparent molecular weight of 37 kDa and a specific activity of 105 U/mg was purified from the culture supernatant. The optimum pH and temperature of Cga-L50 were 8.0 and 75 A degrees C, respectively. The enzyme was stable from pH 6-9 and retained similar to 50 % activity after holding at 85 A degrees C for 10 min. Significant activation of Cga-L50 was observed with K+, Ca2+, Co2+, and Na+; whereas, the enzyme activity was inhibited by Sr2+, Mn2+, Fe2+, Cu2+,Cd2+, Mg2+, and EDTA. Cga-L50 is an endo-type lambda-carrageenase that hydrolyzes beta-1,4-linkages of lambda-carrageenan, yielding neo-lambda-carrabiose as the main product. This study is the first to present evidence of thermostable lambda-carrageenase from hot spring bacteria.