Novel phenothiazine–dithiocarbamate analogues were designed by molecular hybridization strategy and synthesized and evaluated for their anticancer activity in vitro against three selected cancer cell lines (EC-109, MGC-803, and PC-3). The preliminary structure–activity relationship (SAR) for this phenothiazine–dithiocarbamate hybrids is explored. Among all analogues, 2-oxo-2-(10H-phenothiazin-10-yl)ethyl 4-ethylpiperazine-1-carbodithioate (8a) showed the most potent inhibitory activity with an $$\hbox IC}_50}$$ value of $$11.59\,\upmu \hbox M}$$ against PC-3 cells. In addition, compound 8a could arrest the cell cycle at the G1 phase and regulate the expression of G1 checkpoint-related proteins, suggesting that phenothiazine–dithiocarbamate hybrids might be useful as cell cycle blockers.