Essential (volatile) oil from aerial parts of Tamarix aphylla (L.) H.Karst. (Tamaricaceae) grown wild in Jordan was hydrodistilled by Clevenger apparatus and analyzed by means of GC and GC-MS techniques. In vitro screening of potential cytotoxicity of the aqueous (AE) and ethanol (EE) extracts was also evaluated against human breast adenocarcinoma (MCF-7), colorectal adenocarcinoma (Caco-2), and pancreatic carcinoma (Panc-1) cancer cell lines as well as normal human fibroblasts. GC-MS analysis of T. aphylla EO revealed its richness in nonterpenoid nonaromatic hydrocarbons (52.39%), with predominance of 6,10,14-trimethyl-2-pentadecanone as the principal component. Biologically, the plant extracts exhibited cytotoxicity effects in dose-dependent manner against most of the tested cell lines, but potent effects were only predicted against MCF-7 cells with IC50 values of 2.17 ± 0.10 and 26.65 ± 3.09 μg/mL for T. aphylla AE and EE, respectively. T. aphylla AE demonstrated a comparable cytotoxic effect with that offered by the control drug cisplatin (IC50 value of 1.17 ± 0.13 μg/mL), even with higher safety profile against normal fibroblast cells (IC50 values of T. aphylla AE versus cisplatin: 79.99 ± 4.90 versus 9.08 ± 0.29 μg/mL). T. aphylla extracts could be a valuable source for cytotoxic agents with high safety and selective cytotoxicity profiles. Unfortunately, no antiproliferative potential against Caco-2 or Panc-1 cancer cell lines was detected at a concentration less than 30 μg/mL.