Antioxidant properties and phenolic acid content in the pulp of five pumpkin species were evaluated. The following species cultivated in Poland were included: Cucurbita maxima ‘Bambino’, Cucurbita pepo ‘Kamo Kamo’, Cucurbita moschata ‘Butternut’, Cucurbita ficifolia ‘Chilacayote Squash’, and Cucurbita argyrosperma ‘Chinese Alphabet’. The content of polyphenolic compounds was determined by ultra-high performance liquid chromatography coupled with HPLC, while the total content of phenols and flavonoids and antioxidant properties were determined by spectrophotometric methods. Ten phenolic compounds (protocatechuic acid, p-hydroxybenzoic acid, catechin, chlorogenic acid, caffeic acid, p-coumaric acid, syringic acid, ferulic acid, salicylic acid, kaempferol) were identified. Phenolic acids were the most abundant compounds; the amount of syringic acid was found to be the highest, ranging from 0.44 (C. ficifolia) to 6.61 mg∙100 g−1 FW (C. moschata). Moreover, two flavonoids were detected: catechin and kaempferol. They were found at their highest level of content in C. moschata pulp (catechins: 0.31 mg∙100 g−1 FW; kaempferol: 0.06 mg∙100 g−1 FW), with the lowest amount detected in C. ficifolia (catechins: 0.15 mg∙100 g−1 FW; kaempferol below the limit of detection). Analysis of antioxidant potential showed significant differences depending on the species and the test used. The DPPH radical scavenging activity of C. maxima was 1.03 times higher than C. ficiofilia pulp and 11.60 times higher than C. pepo. In the case of the FRAP assay, the multiplicity of FRAP radical activity in C. maxima pulp was 4.65 times higher than C. Pepo pulp and only 1.08 times higher compared to C. ficifolia pulp. The study findings show the high health-promoting value of pumpkin pulp; however, the content of phenolic acids and antioxidant properties are species dependent.