The study on protein requirement of young Siamese spiny eel, Macrognathus siamensis (GÜnther, 1861) was conducted using six different protein level (35, 40, 45, 50, 55 and 60 % protein) with average gross energy of 450 kcal·100/g. The results demonstrated the maximum specific growth rate (SGR), % weight gain and daily weight gain were achieved at 55% protein while the fishes fed with 35% protein was the lowest. It was estimated by broken line regression that dietary protein level producing maximum growth was 46.50% protein. There was no significant difference (P>0.05) on survival rate amongst treatments. Protein efficiency ratio (PER) and apparent net protein retention (ANPR) were not significantly (P>0.05) affected by diet protein levels. No significant (P>0.05) effect of dietary protein levels was found on carcass moisture, crude protein, crude lipid and ash. However, carcass moisture, protein and ash were apparently increased in all fish groups after feeding trial, comparing to fish before the experiment. [ABSTRACT FROM AUTHOR]