Synthesis, structure elucidation and anticancer activities of novel fused 1,2,4-triazine aryl derivatives containing the ethoxycarbonyl (6–10) and carbohydrazide formations (11–15) are presented. Molecular structures of the synthesized compounds were confirmed by IR, ¹H NMR, ¹³C NMR, EI-MS spectra and elemental analyses. Antitumour activities in vitro for heterobicyclic hydrazides of the type 11–14 were evaluated by BrdU method for human LS180, SiHa and T47D carcinoma cells. Amongst them, hydrazide 14 has exhibited remarkable inhibitory effect against SiHa and LS180 tumour cells, and simultaneously was found to be non-toxic towards the human normal cell line – HSF cells. Furthermore, the pulse field gel electrophoresis experiment was performed for characterizing DNA-cleaving activity of heterobicycle 14. The DNA fragments of 2500, 2000 and 500 kilobase pairs (kbp) were commonly detected in the cancer cell lines (SiHa, LS180 and T47D) treated with compound 14. DNA fragmentation pattern, since three types of fragments induced by the tested hydrazide of the type 14 were detected, suggesting a way of interaction with DNA. It is worth pointing out, that DNA strand breaks were also produced in human breast cancer (T47D) cells, a cell line where the induction of DNA fragmentation is very difficult. Moreover, the statistically significant apoptotic activity in T47D human breast cancer cells for the tested heterobicycle 14 was proved using the annexin V – binding assay. The antiproliferative properties in vitro for compounds 6–14 were evaluated by MTT method for human leukaemic Jurkat cells. Significant viability decreases in Jurkat cells treated with different concentrations of compounds 10 and 11 were observed, suggesting that these derivatives have antiproliferative activities. Their acute toxicities were established. For these compounds the influence on the central nervous system of mice in behavioural tests was examined. Molecular structure for free base of the intermediate 4 was confirmed by ¹H–¹H COSY, HMBC and HMQC correlations.