As a kind of thermoplastic materials, nylon-type polymers have been widely used in automotive, electronics, micro-electronics areas due to their excellent mechanical properties. However, such polymers are apt to absorb moisture from ambient air, leading to expansions in volume and variations in mechanical properties. Therefore, it is of great importance to investigate the effect of hygroscopicity on the cyclic deformation of nylon-type polymers, which are often subjected to certain types of cyclic loading in their engineering applications. In this work, the uniaxial ratchetting behaviors of nylon-type polymers (typically for nylon-6, i.e. the PA6 polymer) are investigated by performing a series of uniaxial stress-controlled cyclic tests at different relative hygroscopicities (e.g. 0, 1.0% and 2.12%) to evaluate the effect of relative hygroscopicity on uniaxial ratchetting. Tests are also conducted with different durations of peak stress hold time (e.g. 0 s, 5 s and 10 s) to address the time-dependent ratchetting of nylon-type polymers. After the ratchetting tests, the specimens are held for a certain period of time at zero stress to investigate the strain recovery denoted by the ratio of the viscoelastic stain to the total stain of the polymer. The obtained results show that significant ratchetting occurs in the uniaxial asymmetrical stress-controlled cyclic tests of the nylon-6 polymer; and the ratchetting strain of solid-state nylon-type polymer consists of the recoverable viscoelastic and irrecoverable viscoplastic parts. It is also shown that the ratchetting is time-dependent; and the ratchetting strain increases remarkably with the increase of peak stress hold time. More importantly, the ratchetting of nylon-type polymer shows obvious dependence on the relative hygroscopicity; and the ratchetting becomes more remarkable and the irrecoverable viscoplastic strain increases as the relative hygroscopicity increases. These conclusions provide guidance for the applications of nylon-type polymer materials in engineering, and are very important to the construction of corresponding cyclic constitutive models describing the hygroscopicity- and time-dependent ratchetting of nylon-type polymers.