Net income for Toyota's fiscal first half from April to September fell to 81.5 billion yen ($1.04 billion at current rates) from 289.1 billion yen a year earlier.
It swung to an operating loss of 32.6 billion yen for the six-month period, compared with a year-earlier profit of 323.1 billion yen.
The yen has hit post-World War II highs versus the dollar and scaled 10-year highs versus the euro in recent months, eroding the repatriated profits of automakers such as Toyota and making their products less competitive.
The unit has remained high despite attempts by Japan to weaken it through conducting yen-selling market interventions, raising questions as to whether exporters such as automakers should shift more production abroad.
Toyota has been working to restore production levels after the impact of the March earthquake and tsunami hammered output, forcing the shuttering of plants as component supply chains were shattered.
"In Japan and North America, vehicle sales decreased severely compared to the same period last fiscal year due to the large impact of the Great East Japan Earthquake," executive vice president Satoshi Ozawa said in a statement.
Global sales of cars, trucks and buses fell 18.5 percent between April 1 and September 30, Toyota said.
The impact of Thailand's worst flooding in decades has set back post-quake recovery efforts.
Toyota on Tuesday withheld its annual earnings forecast as it continues to assess the impact of flooding in Thailand on its operations.
Toyota has said the Thai floods will mean continued production adjustments at plants in the United States, Canada, South Africa, Indonesia, the Philippines, Vietnam as well as Pakistan and Malaysia.
Shares in Toyota Motor fell 1.68 percent to 2,503 in Tokyo trade ahead of the earnings announcement.
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