A field study was carried out at the National Root Crop Research Institute experimental farm to determine the critical period of weed interference and magnitude of yield loss caused by weed on turmeric in 2008 and 2009 cropping season. Turmeric was subjected to 13 weeding regimes using randomized complete block design with 3 replications. The result showed that turmeric rhizome yield was significantly affected by weeding regime in both years. Yield was found to be increasing as plots were kept weed free up to 12 weeks after planting (WAP) implying that turmeric should be weed free first 12weeks to avoid drastic yield reduction. Under the weed intensity, weeding at 8week after planting (WAP) produced the highest yield of Turmeric rhizome. On the other hand, delayed weeding beyond the 8weeks after planting (WAP) resulted in a noticeable yield depression in turmeric. This implied that the critical period of weed interference was between 8-12weeks after planting (WAP).