Females of most arthropods undergo multiple matings, most often with different males (polyandry) but sometimes with the same male (repeated matings). Arthropod seminal fluid contains components that are known to stimulate their fecundity and fertility. In spider mites, much is known about the paternal effects on offspring phenotypes, but nothing is known about how the age of males affects their fertility. In Tetranychus urticae Koch (Acari: Tetranychidae), the female offspring ratio is known to decrease with time. Here, we attempted to clarify whether the decrease is due to sperm deletion or a decrease in male fertility ability with age. Female age had significantly increase the fecundity. Older virgin females that mated with virgin males produced fewer female offspring. Female age at mating was negatively related to the mating time (= copulation time, sec) but not to the premating time (sec) after introduction of a virgin male. The mating time tended to decrease with increasing age at mating. Male fertility defined as the proportion of female offspring produced, and male fertility declines with male age and number of matings, even no female offspring produced in some cases. These results suggest that increased male age at mating is associated with sperm depletion, which in turn affects the number of progeny as well as the phenotype of the progeny in the subsequent generation.