Exports of organic chemicals rose 12.1% year on year to Y194.5bn in March, but plastics exports slipped 1.1% to Y206.5bn, the preliminary trade data showed.
Japanese export volumes of plastic materials fell 5.6% year on year to 610,269 tonnes in March, according to the data.
Meanwhile, exports of motor vehicles slipped 27.8% year on year to Y601.5bn in March, making it the largest contributor to the decline in total exports, according to the data.
The Japanese automobile industry has been affected by the massive earthquake and tsunami that hit the northeast region of the country on 11 March, with automakers struggling to restore pre-quake production levels on the back of power cuts and parts shortages.
All of Japan's major car production facilities are operating again, but many car factories are running at lower production rates, according to local media reports.
Car giant Toyota has restarted production of all its domestically produced models, while Honda earlier this month restarted limited production at its factories in Sayama and Suzuka.
"While most of our Japan-based suppliers have resumed production, there are a few suppliers that have yet to resolve the challenge to resume their production," Honda said in a statement.
Meanwhile, overseas shipments of electrical machinery, including semiconductors, tumbled 6.9% year on year to Y1,044bn, according to the data.
Overall imports rose 11.9% year on year to Y5,669bn in March, as the trade balance came to a surplus of Y196.5bn.
Among Japan's major export destinations, shipments to China rose 3.8% year on year, while shipments to the US fell 3.4%, according to the Ministry of Finance data.
The 11 March natural disasters has killed and left missing more than 27,000 people, according to official police figures. The Japanese government estimated the damage from the disaster may rise to as much $302bn.
($1 = Y82.43)
