To study the chemical constituents of K. oblongifolia, silica gel column chromatography, MCI and Sephadex LH-20 were used to separate the 70% acetone extract of the stems of K. oblongifolia. The structures of the isolated compounds have been established on the basis of physicochemical and NMR spectroscopic evidence as well as ESI-MS in some cases. Twenty compounds were obtained and identified as heteroclitalignan A (1), kadsulignan F (2), kadoblongifolin C (3), schizanrin F (4), heteroclitalignan C (5), kadsurarin (6), kadsulignan O (7), eburicol (8), meso-dihydroguaiaretic acid (9), kadsufolin A (10), tiegusanin M (11), heteroclitin B (12), (7'S)-parabenzlactone (13), angeloylbinankadsurin B (14), propinquain H (15), quercetin (16), kadsulignan P (17), schizanrin G (18), micrandilactone C (19) and (-)-shikimic acid (20). Compouds 1, 5, 8, 11-15, 18 and 20 were isolated from this plant for the first time. Toxicity of compounds 1-10 were evaluated with zebrafish model to observe the effect on its embryonic development and heart function. The results showed that compounds 7, 9 and 10 caused edema of zebrafish embryo and decreased the heart rate of zebrafish, which exhibited interference effect on heart development of zebrafish.