Soybeans edged lower after rallying 1.4 percent in the last session on the back of strong demand and uncertainty over US yields.
The most-active wheat contract on the Chicago Board Of Trade lost 0.7 percent to $4.46-1/25 a bushel by 1151 GMT, after hitting a session's low of $4.44 a bushel, its lowest since Sept. 20. Wheat closed down 0.7 percent on Friday.
Soybeans lost 0.5 percent to $9.79-1/4 a bushel while corn fell 0.3 percent at $3.52-1/2 a bushel.
"There is some profit-taking in wheat after the market climbed to a one-month high last week," said an India-based agricultural commodities analyst.
"There is no major fundamental change as supplies remain ample. What we need to watch is the weather in the United States where winter crop planting is taking place."
Rainy weather in some Russian regions poses a risk to next year's grain crop, a Russian Agriculture Ministry official said on Friday.
The ministry's pessimistic outlook for the 2018 crop, follows its downbeat predictions about this year's crop. Its forecast is far lower than most unofficial estimates.
The soybean market received support from strong demand.
The US Department of Agriculture confirmed that private exporters sold 190,000 tonnes of US soybeans to Mexico - the 10th daily soybean sales announcement in the last 11 business days.
Uncertainty about the national soybean yield also lent support. The USDA in a monthly report last week raised its US yield forecast to 49.9 bushels per acre, up from 49.4 in August but analysts are not sure about yields until harvest in October.
Forecasts called for showers in parts of the northwest Corn Belt in the next few days but predicted central and eastern portions of the belt should have dry and warm conditions for harvest.
China imported 380,000 tonnes of corn in August, a 14-fold year-on-year jump, as buyers stocked up on cheaper imports after domestic prices of the grain rose, data from the General Administration of Customs showed on Saturday.
Large speculators increased their net short position in CBOT corn futures in the week to Sept. 19, regulatory data released on Friday showed.
The Commodity Futures Trading Commission's weekly commitments of traders report also showed that non-commercial traders, a category that includes hedge funds, trimmed their net short position in CBOT wheat as well as their net short position in soybeans.