The nutritional and antimicrobial activity of Guava seed collected from Mubi and Mararaba main market were investigated. The nutritional and antimicrobial activities were determined by standard methods, while the elemental composition by using Atomic absorption spectrophotometer (AAS). The result revealed that the proximate analysis: protein content, fat, fibre, ash content, moisture and carbohydrate were 7.845 %, 6.280 %, 15.415 %, 8.220 %, 9.250 % and 52.990 % respectively. The result of the mineral composition showed that potassium has the highest value with 3241.532 ± 0.012 mg / 100 g and Magnesium having the least value of 8.525 ± 0.005 mg / 100 g. Also Guava seed contains beta carotene, B1, B2, B3, B5 and vitamin C with 47.530 ± 0.010 µg / 100 g, 0.530 ± 0.010 mg / 100 g, 4.155 ± 0.005 mg /100 g, 0.625 ± 0.005 mg /100 g, 0.325 ± 0.005 mg /100 g and 514.355 ± 0.005 mg / 100 g values respectively. The result of the antibacterial activity against three clinical isolated organisms was Staphylococcus aureus (12.436 ±0.009 mm), Escherichia coli (17.536 ± 0.009 mm) and Sterptococcusfaecalis (4.560 ± 0.006 mm). The minimum inhibitory concentrations (MICs) for Staphylococcus aureus, Escherichia coli, Sterptococcusfaecalis, Candida Albicans and Aspergillus Niger were 5.0, 5.0, 5.0, 10.0 and 10.0 mg / ml respectively. From the result, guava seed can be regarded as a good source of nutrients and also can be used in pharmaceutical industries.