Thirty-seven myopic children were given either 1-2 drops of 1% cyclopentolate or 1% tropicamide twice with 5 min intervals to evaluate the time course and maximal cycloplegic effect of both agents. The other fifteen subjects were given 1% tropicamide initially, then 1% cyclopentolate given after 30 min of maximal effect of tropicamide appeared to evaluate whether the effect of cyclopentolate was superior to tropicamide. Cycloplegic refraction was measured with an auto-refractometer (Topcon RK-3000) before drug delivery and every 15 min thereafter, for 90 min. The maximal cycloplegic effect of cyclopentolate was around 45 min, then it remained stable until 90 min after the last instillation. The effect of tropicamide was faster than that of cyclopentolate. It was around 30 min, then it stabilized until 75 min. The extra effect of cyclopentolate over tropicamide was minimal (only -0.1D). The power of cornea and astigmatism were not affected by either agent. However, a big variation in astigmatism was noted during the course, especially with cyclopentolate. This study suggests that 1% tropicamide should be a good agent for routine refractive status checking on myopic children.