This paper examines the pricing relationship between the mini index futures and the regular-sized counterpart traded on TAIFEX. The mini-regular arbitraging is free from many trading impediments, providing an opportunity to investigate the arbitrage activities in an almost frictionless environment. The mini-regular pricing is highly efficient as evident by the small ex-post mispricing and unpromising ex-ante arbitrage profits. The W-shaped intraday pattern of price deviation suggests that arbitrage opportunities tend to concentrate in periods (futures opening and spot opening) of intensive information impacts. Regression results show that information relevant variables including futures volatility, volume, and open interest are significantly linked to the mini-regular price deviations. Furthermore, we find that the TX-MTX pricing efficiency is improved as the originally lagged mini contract enhances its price discovery so that the two markets respond to information impacts in a synchronous manner.