Dendritic and hyperbranched poly(amidoamines) are the first covered and most investigated photoluminescent polymers carrying unconventional chromogens, and studies reveal that the oxidation or acidification of the N-branched tertiary amine in these compounds is responsible for the light emission. Here, we report the synthesis and photoluminescence properties of novel hydrosoluble aliphatic tertiary amine-containing hyperbranched polysiloxanes (TAHPSi). The as-prepared polymers are fabricated by a mild one-step transesterification reaction using raw materials, including tetraethoxysilane (TEOS), triethanolamine (TEA), N-methyldiethanolamine (NMDEA) and diethylene glycol (DEG). Amusingly, the resultant products, without any treatment, such as oxidation or acidification, can still produce bright blue fluorescence under a UV light, and our rudimentary study manifests that the terminal hydroxyl group plays a key role in forming blue-fluorescent species. In addition, the significant concentration and pH-dependent profiles of luminescence intensity are also observed. Moreover, the TAHPSi can be used to detect metal ions, and there is strong selective quenching in respect of Fe³⁺. Therefore, the TAHPSi show promise as Fe³⁺ probes.