Amine-modified carbon micro/sub-microtubes that encapsulate magnetite cores have been synthesized by decomposing a ferrocene/hexabromobenzene mixture in the presence of ammonia under solvothermal conditions at 250 °C for 24 h in a one-step process. The as-prepared carbon microstructures (NH2-ME-CMTs) were 90–2000 nm in diameter and from tens to hundreds of micrometers in length that could be tuned in various solvents. The surface of the carbon microtubes can be modified with amino groups by the synthetic process, as confirmed by infra-red (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Ammonia in the reaction system plays a key role in the formation of the microtube morphology and was the source of the surface functionalization groups. Fluorescent fluorescein isothiocyanate (FITC) was selected as a model compound and successively attached to the amino groups of the carbon microtubes. This result confirms the reactivity of the amino groups on the surface of the carbon microtubes. The inner magnetite cores were removed after immersion in 1 M HCl solution at room temperature over two months, and hollow carbon microtubes (NH2-H-CMTs) were obtained. The magnetite-encapsulated carbon microtubes and the hollow carbon microtubes were coated on gold electrodes to prepare carbon microtube-modified gold electrodes. The two electrodes have been used to investigate the oxidative properties of dopamine (DA) and ascorbic acid (AA). Different from the magnetite-encapsulated microtube-modified electrode, the hollow microtube-modified electrode can be utilized in the selective detection of DA in the presence of a large excess of AA. The electrochemical behaviour of DA and AA on the hollow carbon microtubes modified with amino groups is similar to that on carbon nanotubes. This result suggests that the one-step synthesis method will not change the electrochemical properties or break the backbone structure of the carbon microtubes.