An oscillator and a clock circuit are disclosed. In an oscillator (100), a tail inductor connected to a cross-coupled transistor includes at least two inductors connected in parallel. Therefore, an inductance of the tail inductor is less than an inductance of any one of the inductors. This can address a design difficulty that a tail inductor with a smaller inductance needs to be used as an operating frequency of a VCO increases. The oscillator (100) includes a first cross-coupled transistor (121) and a first tail inductor (111). The first tail inductor (111) includes at least two inductors connected in parallel. The first tail inductor (111) is coupled to a source of the first cross-coupled transistor (121). The source of the first cross-coupled transistor (121) is coupled to a power supply or a ground through the first tail inductor (111).