Analysts said speculators preferred to cut their holdings in view of downtrend in physical markets.
Muted demand from soap and lubricant industries amid higher supplies from growing belts in spot markets weighed on prices, they added.
At the National Commodity and Derivative Exchange, castor seed for delivery in September month dropped by Rs 49 or 1.07 per cent to Rs 4,548 per quintal, with an open interest of 850 lots.
The most-traded October month contract also fell by Rs 37 or 0.79 per cent to Rs 4,675 per quintal, having an open interest of 91,200 lots.