This study examines the effects of own and spousal health on transitions in loneliness over time among married middle-aged and older adults in China, and explores the possible gender differences in these effects using data from the three waves of the China Health and Retirement Longitudinal Study (2011–2015). The sample includes 6,422 men and 6,391 women who were married and aged 45 and older at the baseline survey. Middle-aged and older adults with poorer physical and emotional health statuses are more likely to transition into and less likely to transition out of loneliness in a two-year period. Spouse's emotional health also affects both types of transition in loneliness and spouse's functional limitation affects transition into loneliness through spouse's emotional health. In addition, for married men, their own functional limitation is significantly associated with their transitions into and out of loneliness. For married women, their spouse's functional limitation is significantly associated with their transition into loneliness and this is mainly through its association with spouse's emotional health. Also, for married women, their spouse's emotional health is significantly associated with their transition out of loneliness. Social interventions to reduce feelings of loneliness need to take a couple approach and consider both spouses’ health problems and how they may affect their daily activities and their interactions with each other and with others.