A BJT (bipolar junction transistor)-based uncooled IR sensor and a manufacturing method thereof are provided. The BJT-based uncooled IR sensor includes: a substrate; at least one BJT which is formed to be floated apart from the substrate; and a heat absorption layer which is formed on an upper surface of the at least one BJT, wherein the BJT changes an output value according heat absorbed through the heat absorption layer. Accordingly, it is possible to provide a BJT-based uncooled IR sensor capable of being implemented through a CMOS compatible process and obtaining more excellent temperature change detection characteristics.