The effect of reaction temperature, time and pH on the maximum total sugar concentration during thermal-acid hydrolysis of sisal boles juice was investigated. The Minitab software (V. 17) was used to design a 2n full factorial design for sisal juice hydrolysis and analyse the effects of the variables on the response. Thermal-acid hydrolysis can be carried out at a moderate temperature of 60°C with a concentrated hydrochloric acid at pH of one within a period of 30 minutes to achieve a sugar yield of 39%. The breakdown of complex sugars to simple sugars of sisal bole juice is basically a function of acid concentration in sugar solution. Lowering pH of the juice contributed to increase in hydrolysis rate. The use of ANOVA analyses gave evidence that linear, 2- way interactions and 3-way interactions of all the variables: temperature (60-100°C), time (30-60 min) and pH (1-5) significantly affected the sugar yield. This amount of sugar yield from sisal boles juice is higher than the yield of 26% which has been reported. The hydrolysed juice was also subjected into fermentation for lactic acid and results showed favourable LA yield was obtained with the recommended thermal-acid hydrolysis in this study.The Tanzania Commission for Science and Technology - COSTECH (Bioplastics Project-UDSM) and DAAD (In-Country scholarship) for financial support.