Oxytocin has been used to treat neurodevelopmental conditions in adolescent patients but possible effects on reproductive development have not been well investigated. The effects of daily intra-nasal oxytocin treatment (12-18 months of age) on puberty and fertility were studied in colony-housed, male and female titi monkeys (Plecturocebus cupreus). Body weight, urinary conjugated pregnanes and estrogens (defining cyclicity) in females, and androgens and sperm in urine of in males, were measured from 1 to 3 years of age to detect puberty. Serum testosterone was also measured in males at 13, 23 and 33 months of age and hemi-castration at 3 years of age enabled assessment of testicular morphometry and oxytocin receptor expression. An oxytocin treatment*time interaction suggested a minor, transient suppression in weight gain after treatment ended. Note that females weighed 10% less across all ages. Oxytocin-treated females exhibited early, spurious ovulations but neither regular cyclicity (≈30 months) nor pregnancies were affected by treatment. Oxytocin did not affect the pubertal increase in urinary androgen or the first appearance of sperm, which occurred as early as 15 months of age. Treatment did delay the puberty-associated rise in serum testosterone in males. All males were pubertal by 22 months and all females by 32 months of age. Although no major male or female fertility outcome was observed, oxytocin demonstrated some physiological effects through a delay of testosterone secretion in males, induction of precocious ovulation in females, and a suppression of general weight gain for the months following treatment.