Objectives: This study aimed to determine the effectiveness of guyabano fruit and pineapple extract in the fermentation process of vinegar. Methodology: Pineapple and guyabano fruits were gathered from Alilem, Ilocos Sur, Philippines. Three treatments and three replications were formulated, respectively. Each treatment had 1000 mL newly made sugarcane wine (basi). T1 contained 250 g chopped guyabano fruit plus 25 mL pineapple extract. T2 had 500 g guyabano fruit plus 50 mL pineapple extract;

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... le T0 was untreated. Experimentation was done at the Regional Science High School but the analyses of the samples were done at the Department of Science and Technology (DOST), Regional Office No. 1 DMMMSU-MLU Campus, City of San Fernando, La Union. For the acceptability of the preparations, twenty (20) people from Alilem, Ilocos Sur were randomly selected to evaluate their tastes. Findings: Results showed that after one month of storing, the mean percentages of T0, T1, and T2 were 0.633%, 1.12%, and 1.07%, respectively. Based from all the results, it was found out that T1 garnering 1.12% yielded the best result among the three treatments in terms of acetic acid content and taste acceptability but it is lower than the typical acetic acid of vinegar which is 4%. ANOVA and Friedman test showed that there is no significant difference between the treatments in terms of acetic acid content and acceptability, respectively. Conclusion: Guyabano fruit and pineapple extract have effects in fermentation process of vinegar but ineffective in enhancing the duration of fermentation process of vinegar.