This article aims to examine in how far female immigrant and native part-timers have the same opportunities and risks in terms of job transitions. In particular, we study the probability of moving from a part-time job to a full-time job, to unemployment or to inactivity. To do so, we use panel data from the Spanish Labour Force Survey between 2008 and 2016. The first preliminary results show that our assumption holds, that with a decline in working hours also the job prospects get worse. Although this pattern is common for both immigrants and natives, we find ethnic gaps along the working hour distribution. On the one hand, female Spaniards in marginal part-time employment are more likely to leave the labour force than foreign-born workers, whereas those employed in short part-time work are less likely to move to full-time jobs. These penalties can be explained by a negative selection of native old-employees. On the other hand, the higher the working hours, the larger the immigrant disadvantage in terms of avoiding unemployment and inactivity. The overrepresentation in the secondary segment of the labour market explains their higher insecurity in the substantial part-time work. Finally, differences in education, family context, and period have little influence on the ethnic gaps found.